Form
If + S + Present Simple, S + will/won’t + Verb.
If it rains tomorrow, we will stay at home.
You will miss the bus if you don’t leave now.
Meanings
A Real and Possible Future Condition
We use the First Conditional to talk about a future situation that is realistic and possible. We are predicting the likely result if the condition is met.
Compare with Zero Conditional:
Zero: If you heat ice, it melts. (Always true, a fact).
First: If it is sunny tomorrow, we will go to the park. (A specific plan for a possible future).