Until as a preposition means ‘up to (the time that)’:
We played chess until midnight. (up to midnight)
The film didn’t end till eleven
Until as a conjunction
We use until as a subordinating conjunction to connect an action or an event to a point in time:
Let’s wait here till the rain stops. (till + subordinate clause)
We use present verb forms to refer to the future after until:
I can’t wait until the summer holidays begin.
We also use the present perfect after until to refer to actions or events that will continue up to a point in the future:
We’ll sit here till Donna has finished.
We use the past simple and past perfect to talk about events in the past:
He was the headteacher until he retired in 1968.