If you are 100% sure that something will happen, you can use the following "zero conditionals":
If + [Subject] + [Base Verb], [Subject] + [Base Verb].
For example:
If ice melts, It becomes water.
But if you are not so sure, you can use "first conditionals":
If + [Subject] + [Base Verb], [Subject] + [Modal] + [Base Verb].
For example:
If I go to the movies, I will/may/might/could eat popcorn.