Conditional sentences have two clauses: an IF clause that presents a condition and a MAIN clause that presents the resulting outcome. The IF clause uses verbs like "If + present simple" or "If + past simple" while the MAIN clause uses modal verbs like "will", "would", "could", or "might" followed by a future form or past participle to indicate the consequence if the condition is met. Examples provided demonstrate how the clauses are structured depending on whether the IF clause or MAIN clause comes first.