The document discusses two types of conditional sentences:
Type I conditional sentences use "if + present simple" in the if-clause and "future simple" in the main clause to talk about probable future situations.
Type II conditional sentences use "if + past simple" in the if-clause and "conditional (would + infinitive)" in the main clause to give advice or talk about imaginary or improbable situations. Examples are provided to illustrate the structures of each type of conditional sentence.