The first conditional has the present simple after 'if', then the future simple in the other clause:
It's used to talk about things which might happen in the future. Of course, we can't know what will happen in the future, but this describes possible things, which could easily come true.
For example (zero conditional): if you sit in the sun, you get burned (here I'm talking about every time a person sits in the sun - the burning is a natural consequence of the sitting)
But (first conditional): if you sit in the sun, you'll get burned (here I'm talking about what will happen today, another day might be different)
First vs. Second ConditionalThe first conditional describes things that I think are likely to happen in the future, whereas the second conditional talks about things that I don't think will really happen. It's subjective; it depends on my point of view.
For example (first conditional): If she studies harder, she'll pass the exam (I think it's possible she will study harder and so she'll pass)
But (second conditional): If she studied harder, she would pass the exam (I think that she won't study harder, or it's very unlikely, and so she won't pass)