If-clauses are also known as conditional clauses or conditional sentences.

This means that the event in the main clause (not counting the if) only takes place if the condition in the clause containing if is fulfulled

Conditional type 0

Is used to talk about general truths, scientific facts or things which always happen under certain conditions

If clause (condition), main clause (resolut)

if + simple present, simple present

The zero conditional is also often used to give instructions, using the imperative in the main clause.

• If Bill phones, tell him to meet me at the cinema
• Ask Pete if you're not sure what to do
• If you want to come, call me before 5:00
• Meet me here if we get separated

Conditional type 1 - Real Conditional

Used for something that is likely to happen

"If you don't hurry, you'll miss the train"

"If I don't see her in class, I'll call her"

If clause (condition), main clause (result)

if + simple present, simple future