This is actually quite complicated, but I will give you the simplified version that is taught to people learning English as a second language. (Information adapted from A Basic English Grammar with Exercises by John Eastwood and Ronald Mackin, Oxford University Press 1988.)
When you use if you are usually starting a conditional clause — also called an adverbial clause of condition or an IF-clause. You do this to show cause and effect, or what MIGHT happen if something else happens. There are three main kinds of IF-clause:
1. Type 1: IF + simple present tense, then + will, can, may/might.
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