Two simultaneous things may take place at the same time.
While something was happening, something happened.
Contrast or Contrary
Good or bad may happen as a result.
Although I knew it was risky, I decided to accept the proposal.
One thing does or does not allow another thing to take place.
Because I was looking at the sea, I did not her her coming.
A real or an imaginary situation where something would have acted upon or not.
If I was having shower, I could not take the call. (Imaginary)
I could take the call, if I had not had the shower. (Real)