2) Till is a contraction of until (and I believe that in the past some people put an apostrophe at the beginning of the word to show the missing letters. That seems to have gone out of fashion.)
3) Many people spell it "til".
They are interchangeable although "till" is less formal.
It's only five months until Christmas.
There's only eight months to go till my birthday.
I'm not buying you a present until you say sorry.
He'll be at the party till about midnight.
Student or Learner