Is there a good extensive Summary about If-Sentences, because the more I read the more I get confused

I've found the following basic structures:
Type 1 (realistic)
if+simple present or present progressive - will future / simple present / going to future
Type 2 (unrealistic)
if+simple past or past progressive - would infinitive / would have past participle / would have been present participle
Type 3 (impossible)
if+past perfect or past perfect progressive - would infinitive / would have past participle
So. The stuff above confusing enough, I have encountered, that there are modal verbs too..
I found this on the internet, why is this correct when it's not allowed to use would (or could/might) in the main clause an/or would in an type 1 sentence?
"It would be cool, if I could."
I would have said: "It will be cool, if I can" or "It is cool, if i can"
Could someone elaborate this topic a little bit further or send me to a comprehensive internet-website. This stuff is driving me CRAZY!
(In germany back in school we had learned only about three types of if...these were the times back than

)