FIRST CONDITIONAL :
If + present tense with will
-- talk about probable or possible present or future situations
* If I leave at 5.30, I will be there at 6.15.
If + past tense with would
-- talk about unreal situations or improbable present or future situations
* If I were the manager, I would introduce a coffee break
If + past perfect tense with would have + past participle
-- to talk about unreal situations in the past and their result
* If I had seen you, I would have said hello but I didn't see you.