A conditional sentence is a sentence structure commonly used in English to talk about something (a result) that may happen ONLY IF something else happens first (a condition). The condition may be something real or unreal/hypothetical, and the result could a definite result, or just a possible/likely result.
The most common type of conditional sentence uses if. These are the easiest conditional sentences to form and understand. You could also use unless, when, after, before or as soon as. Here, we will focus on using conditional sentences with if.