Just to add to what others have told you already...
As you know, verbs in Russian are of two aspects, perfective and imperfective, and the addition of a prefix often makes them imperfective.
One of the mistakes that I made when I started out was presuming that every verb in English would have both an imperfective and perfective form in Russian too. This isn't always the case. For example, "to know" in English always has an imperfective meaning, you can't suddenly "know" something, you will "find out" something (узнать), realise (понять) or recognise (признать) it. (Of these, the first two are most common)
Other common examples of this which spring to mind are искать/найти (to look for / to find), сдавать/сдать экзамен (to take / pass an exam), ловить/поймать (to try to catch, to fish / to catch), работать / заработать (to work / earn)
You can then often make a new imperfective from the prefixed verb. So работать = to work (impf), заработать = to earn (pf.) and зарабатывать = to earn (impf.)
говорить = to speak, talk; уговорить = to persuade (impf.), уговарывать = to persuade (impf.)
In many cases, of course, the prefix doesn't affect the translation, it rather denotes the start of an action or the duration of the action.
Мы тут простояли около 40 минут (My god - we were there for 40 whole minutes!)
Мы тут постояли около 40 минут (We were only there for 40 minutes or so)
Всю ночь собака выла и выла (The dog howled and howled all night)
Услышав шаги, собака завыла. (On hearing the footsteps, the dog started howling.)
The aspect system is one of the most difficult things to master in Russian (a bit like phrasal verbs in English), but it's always something which makes the language special - it allows economising on words and introduces nuances that would normally expressed with additional words.
If you're confused about prefixes, it's often best to look in a specialist verb dictionary or grammar (i like Derek Offord)... or ask on here.
Espero que lo que he escribido te ayuda.
NOW, the (wo)man who can help me with the Latvian verbal system will be truly deserving of a Guinness.