THE ZERO CONDITIONAL
Is used for when the time being referred to, is now or always and the situation is real and possible.
Is often used to refer to general truths.
The tense in both parts of the sentence is the simple present.

First Conditional
Refers to a possible condition and its probable result. These sentences are based on facts, and they are used to make statements about the real world, and about particular situations. We often use such sentences to give warnings.
The time is the present or future and the situation is real.

Second Conditional
Refers to an unlikely or hypothetical condition and its probable result. These sentences are not based on the actual situation.

Third Conditional
Refers to an impossible condition in the past and its probable result in the past. These sentences are truly hypothetical and unreal, because it is now too late for the condition or its result to exist.