The first conditional is used to talk about a possible future situation and its
result. a VERY LIKELY situation (the condition) and the consequences(or
the result) of it.
If + present simple, will + base verb
If the global warming gets worse, the planet won't repair itself.
When we use will in the result clause of the
first conditional, we are certain that
something will happen. It is definite.
I'm not feeling very well. If it rains tomorrow, I'll
stay at home.
We can use may or might instead of will. This means
that the consequence is not certain. It is possible, but
not definite.
I'm feeling fine and I've got a car. If it
rains tomorrow, I might stay at home, or I
may go shopping. I'll decide tomorrow.