The document discusses different conditional sentence structures in English:
- Zero conditional for facts that are always true using the present simple tense.
- First conditional for possible future events using "if + present, will/may/might + verb".
- Second conditional for hypothetical or unlikely present situations using "if + past simple, would + verb".
- Third conditional for impossible past situations using "if + past perfect, would have + past participle". Examples are provided for each conditional along with explanations of their structures and uses.