We use the first conditional to talk about real or possible future situations, to make predictions, offers, suggestions, etc.
If you eat that, you will be ill.
If she needs a car, she can borrow mine.
I’ll stay at home if it rains.
The structure of the first conditional is:
If/when + present simple – will + infinitive.
The “If-clause” is the conditional clause and the other clause(s) is the “main clause” (or “result-clause”) which tells the result.
It is not unusual to use the first conditional structure with: in case, unless, as long as, as soon as instead of “if”
In case you don’t get back by 10, I’ll call the police.
We’ll go for a walk unless it rains.
We will start eating as soon as Juli arrives.
Note: use a comma at the end of an if-clause when an if-clause is at the beginning of the sentence.

Click here to find the lesson about the zero conditional.
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