There are three types of conditionals, plus the "mixed conditionals" (a mixture of the Second and Third Conditionals).

The conditional clause usually starts with the conjunction "if".

First Conditional: If + Present Simple + Will + Bare Infinitive (Likely to happen).
Second Conditional: If + Past Simple + Would + Bare Infinitive (Unlikely/More Polite).
Third Conditional: If + Had + Past Perfect + Would Have + Past Participle (Impossible).

There is another variation using "if only" (for example, "if only I had more money.")

As well as the pure conditionals, there are also two kinds of mixed conditionals. They are in fact variations of the third conditional, but relate to present conditions instead of the past.

Mixed Conditional #1: If + Had + Past Perfect + Would/Could/Might + Infinitive (Impossible Present Effects).
Mixed Conditional #2: If + Be + Would Have + Past Participle (Impossible Past Effects).