RXJS OBSERVABLES | What is Observable ? For Beginners or Advance

I will try to explain in most simplest way following questions
What is Observable ?
Observable are Sync or Async ?
Observable are like Events or Promise ?
What is Hot Observable and how it differ from Cold Observable ?
How Observable execute ?
Why should we unsubscribe Observable ?

[evans]

i feel lucky to live in such a great time

[ShubhamBhardwajprofile]

Its Awesome but some more explanation is required on moving from promises to observable and regarding subject. only that interval.Anyways thanks.