Conditional sentences consist of two clauses:
The if clause which includes the condition: If I have time
and the main clause which includes the result: I will help you
The order of the clauses does not change the meaning.
If I have time, I will help you. = I will help you if I have time.
It is also possible to use this structure with some other words instead of if, such as: unless, as long as, when, as soon as, or in case.
I will help you as long as I have time.