the first conditional talks about thing that will probably happen now or in the future. if/present tense. will/can/may+bare infinitive note that unless can be used in this conditional. unless means the same as if not.
we use the second conditional to talk about things
that probably won't happen.
if+ past tense. would/could/might+bare infinitive.
we use the third conditional to talk about the past. it always talks about hypothetical things because we cannot change the past. if+past perfect. would/could/might+have+past participle.