We use Zero Conditional to talk about actions and situations or conditions that always lead to the same results or consequences.
The form is:
If + Present Simple, .... Present Simple.
If water reaches 100 degrees, it boils.
If I eat peanuts, I get allergy.
First Conditional is used to talk about possible future events or consequences which depend on other future events or conditions.
The form is:
If + Present Simple, .... Future Simple.
If she gets good marks today, they will go to the park.
If you are late, we will go without you.