The structure of a first conditional sentence
A first conditional sentence consists of two clauses, an "if" clause and a main clause:

if clause main clause
If you study hard, you will pass the test.

If the "if" clause comes first, a comma is usually used. If the "if" clause comes second, there is no need for a comma:

main clause if clause
You will pass the test if you study hard.

We use different verb forms in each part of a first conditional:

main clause if clause
You will pass the test if you study hard.

2. Using the first conditional
The first conditional is used to talk about things which are possible in the present or the future — things which may happen:

Example Explanation
If it's sunny, we'll go to the park. Maybe it will be sunny — that's possible.
Paula will be sad if Juan leaves. Maybe Juan will leave — that's possible.
If you cook the supper, I'll wash the dishes. Maybe you will cook the supper — that's possible.