A conditional sentence is a sentence in which one thing depends on another.
The two clauses can be swapped around.
If I ride my bike every day I will get fit.
I will get fit if I ride my bike every day.
We sometimes use a comma if the conditional part of the sentence comes first.
If I ride my bike every day, I will get fit.
Other conjunctions can be used in conditional sentences as well as 'if'.
Provided it doesn't rain we will go to the beach tomorrow.
You can't go out to play unless you finish your homework.
As long as it doesn't snow the school will remain open.