Conditional Tense- If/when.
Zero conditional- real situation as:
sub+base verb / sub+ base verb
Eg: If ice melts, it becomes water.
First conditional- probability
If+sub+Base verb/ sub+model (would,may,might,shall)+Base verb
Eg: If I go to the movie,I may eat popcorn.
Second conditional- unreal situations
If+Sub+past verb/ sub+would+Base verb
Eg: If I had a million dollars, I would give you most of it.
Third conditional- changing an event in the past
If+sub+past perfect/sub+ would have+past participle
Eg: If you had slept earlier, you would not have felt tired.