I'd heard of propositional logic for years, but until I came across this question, I'd never heard of predicate logic.  Moreover, the fact that Introduction to Logic: Predicate Logic and Introduction to Logic: Propositional Logic (both by Howard Pospesel) are distinct books leads me to believe there are significant differences between the two fields.  What distinguishes predicate logic from propositional logic?
Propositional logic (also called sentential logic) is logic that includes sentence letters (A,B,C) and logical connectives, but not quantifiers. The semantics of propositional logic uses truth assignments to the letters to determine whether a compound propositional sentence is true. 

Predicate logic is usually used as a synonym for first-order logic, but sometimes it is used to refer to other logics that have similar syntax. Syntactically, first-order logic has the same connectives as propositional logic, but it also has variables for individual objects, quantifiers, symbols for functions, and symbols for relations. The semantics include a domain of discourse for the variables and quantifiers to range over, along with interpretations of the relation and function symbols.

Many undergrad logic books will present both propositional and predicate logic, so if you find one it will have much more info. A couple of well-regarded options that focus directly on this sort of thing are Mendelson's book or Enderton's book. 

This set of lecture notes by Stephen Simpson is free online and has a nice introduction to the area. 
