The zero conditional is used to talk about things that are generally true or things that always happen under certain conditions.
It’s called “zero” because it doesn’t involve any hypothetical or imaginary situations.

Positive: If + subject + present simple, subject + present simple
Negative: If + subject + do/does not + present simple, subject + infinitive
Question: If + subject + present simple, do/does + subject + infinitive?

Common uses:

1. To talk about things that are always true under certain conditions

• If you heat water to 100 degrees Celsius, it boils.
• If you don’t water plants, they die.
• If you mix red and blue paint, does it become purple?

2. To give instructions or directions

• If you are hungry, make a sandwich.
• If you don’t have water, you can’t make tea.
• If I burn the bread, does it taste bad?

3. To talk about habits or routines

• If I wake up early, I exercise before work.
• If I don’t set an alarm, I oversleep.
• If you go for a run, do you feel good?