This document discusses the four main types of conditionals used in English:
1) First conditional deals with real possibilities involving the future using "if + present + future" form.
2) Second conditional involves not real possibilities using "if + past + would" form, like fantasizing.
3) Third conditional refers to impossible past events using "if + past perfect + would have" form.
4) Zero conditional always states scientific facts using simple present tense like "if + present, + present" form.