You can read Alcibiades Minor online in English at The Perseus Project or in French in Cousin's translation or in Chambry's translation at Wikisource.
The dialogue is an apparently private discussion between Socrates and Alcibiades.
The Plot and The Thought
Socrates opens the discussion by asking whether Alcibiades is going to prayers, which he says he is. Socrates remarks that "there is a great need for caution, for fear you might, all unawares be praying for great evils when you think you are asking for great goods" (138b). He uses the example of Oedipus praying that his sons would take arms in order to determine their inheritance, which they did -- against each other. Alcibiades remarks that this would be what a madman would do. Socrates argues, however, that it's really stupidity that's the issue, and that stupidity is a matter of not knowing what should be done and said.
He asks Alcibiades to imagine that the god appeared to him and offered him sole rulership of Athens, or perhaps even all of Europe, plus universal recognition of this rule. He would presumably go home happy; and Alcibiades agrees. But then, Socrates, asks, would he do this if the cost were his life, and Alcibiades replies that he would not, because then it would be useless to him. Thus we see that even something like becoming ruler of the world is something we only want if it is really good for us, and not at the expense of our lives or other things like that. Socrates wonders if perhaps human beings are wrong to blame the gods for misfortunes; perhaps it is instead their own stupidity in not asking for the right things that is the problem.
Alcibiades agrees that this is all well said, but suggests that ignorance is often the real problem. But Socrates points out that it wouldn't be ignorance as such but ignorance of what is best. Ignorance could even be a good if it kept you from doing some wicked thing. Someone without knowledge of what is best, however, is no good to anyone, including himself.
Socrates discusses the example of the Spartans, who only pray for the good and noble, and not anything else, and tells a story. Sparta and Athens were fighting, and Athens sent to the oracle of Ammon in Libya to ask why the Spartans kept winning when Athenian sacrifices were better, Athenians feasts in honor of the gods were better, and so forth. And the answer came back (149b): "Thus saith Ammon to the Athenians: I prefer the terse Laconic utterance to all the sacrifices of the Greeks." Thus he concludes:
It would be a strange and sorry thing if the gods took more account of our gifts and sacrifices than of our souls and whether there is holiness and justice to be found in them....Gods and men of sound men are more likely to hold justice and wisdom in especial honor; and none are wise and just but those who know how to behave and speak to gods and men. (149e-150a)
Alcibiades agrees, but Socrates then suggests that the implication is that he shouldn't pray until he learns how to behave to gods and men. Alcibiades asks Socrates to teach him, giving him the victory-garland on his own head, and Socrates ends the dialogue remarking that he looks forward to victory over Alcibiades' other lovers.
* The dialogue clearly has ties both to Alcibiades Major and to Xenophon's Memorabilia. Hutchinson discusses the relation to the first in his introduction to the dialogue in the Complete Works (p. 596):
Alcibiades, full of ambition, encounters Socrates, who engages him in a conversation and makes him realize how little he understands of what he needs to understand; at the end Alcibiades is humiliated and begs Socrates to be his teacher and lover. To this schematic extent Second Alcibiades tells the same story as the Alcibiades also preserved in the Platonic corpus. Certain other parallels suggest that the author of Second Alcibiades adapted Alcibiades 141a-b ≈ 105a-c; 145b-c ≈ 107d-108a. But perhaps the similarities between the two dialogues are to be explained by their common derivation from the celebrated Alcibiades of Aeschines of Sphettus, or from one of the other dialogues called Alcibiades. We cannot determine this question, because Aeschines' dialogue survives only in fragments, and the Alcibiades dialogues of Euclides and Antisthenes, other students of Socrates and writers of Socratic dialogues, are lost.
In addition, the same topic found here comes up in the Athenian's discussion of religion in Laws III (687d-e):
Athenian: Yet the father will often pray the gods that the things which the son prays to obtain may in no wise he granted according to the son's prayers.
Megillus: Do you mean, when the son who is praying is still young and foolish?
Athenian: Yes, and also when the father, either through age or through the hot temper of youth, being devoid of all sense of right and justice, indulges in the vehement prayers of passion (like those of Theseus against Hippolytus, when he met his luckless end), while the son, on the contrary, has a sense of justice,—in this case do you suppose that the son will echo his father's prayers?
Megillus: I grasp your meaning. You mean, as I suppose, that what a man ought to pray and press for is not that everything should follow his own desire, while his desire in no way follows his own reason; but it is the winning of wisdom that everyone of us, States and individuals alike, ought to pray for and strive after.
On the side of Xenophon, we can see a clear connection to Xenophon's Memorabilia 1.3.2:
And again, when he prayed he asked simply for good gifts, “for the gods know best what things are good.” To pray for gold or silver or sovereignty or any other such thing, was just like praying for a gamble or a fight or anything of which the result is obviously uncertain.
One can even find people in the nineteenth century suggesting that the work was written by Xenophon, although this never was regarded as especially plausible.
* The oracle of Ammon was the foreign oracle the Greeks most trusted. The reason Athens would be consulting this oracle is either (1) they couldn't reach Delphi because of fighting with the Spartans or (2) it was especially associated with the Spartans, who regarded it quite highly.
* Socrates' piety is presented many different ways in Plato; we have Socrates' daemon or daimonion (mentioned in Phaedrus, Ion, Meno, Euthydemus, Theaetetus, Euthyphro, and Apology), the engagement with the oracle at Delphi (mentioned in Apology), the way he understands his expertise in erotics (mentioned in Phaedrus and Symposium), Socrates' divinatory dreams (mentioned in Apology, Crito, and Phaedo), his writing of a hymn to Apollo (mentioned in Phaedo), and his participation in sacrifices (mentioned in Phaedo). We also have about a dozen cases of Socrates praying in those dialogues generally recognized as authentic. B. Darrell Jackson in "The Prayers of Socrates" [Phronesis, Vol. 16, No. 1 (1971), pp. 14-37] lists them as such:
(1) Euthydemus 275d -- to the Muses and Memory, for aid in remembering a conversation
(2) Phaedo 117c -- to the gods, as he takes hemlock, for a happy migration
(3) Symposium 220d -- to the sun, after the twenty-four hour 'trance' at Potidaea
(4) Phaedrus 237a-b -- to the Muses, for aid in his first speech on love
(5) Phaedrus 257b -- to Eros, at the close of his second speech on love, for forgiveness, success in love, and intercession
(6) Phaedrus 278b -- to be a philosopher
(7) Phaedrus 279b-c -- to Pan and others, for inner beauty, wisdom, temperance, and harmony
(8) Republic I, 327a-b -- Socrates tells of having prayed at the festival of Bendis
(9) Republic IV, 432c -- Socrates prays for success in discovering the nature of justice
(10) Republic VIII, 545d-e -- to the Muses, for information on the origin of political dissension
(11) Philebus 25b -- to a god, for aid in the argument
(12) Philebus 61b-c -- to Dionysus and Hephaestus, for success in the argument
(Some of these are clearly stylistic, according to conventions, but some are more substantive.) We find, then, that Socrates in Plato's dialogues prays to the gods for (1) help in exploring the nature of love, justice, goodness, and the like, (2) a good death, and (3) spiritual qualities like wisdom or the love that pursues wisdom. This is obviously consistent with the position taken in this dialogue, and sheds some light on it.
Quotations are from Anthony Kenny's translation in Plato, Complete Works, Cooper & Hutchinson, eds., 596-608.