Zero Conditional

If + PRESENT, PRESENT
We use Zero Conditional to talk about things that are always or usually true.
Eg:

If you heat water to 100 degrees, it boils.
If I drink milk, I feel sick.

First Conditional

If + PRESENT, FUTURE
We use First Conditional to talk about a specific future.
Eg:

If you have a party on Saturday, I'll come.
If you eat that meat, you will get sick.