It's used to emphasize the necessity of an event to occur in order for another event to occur. Both conjunctions mean the same thing:
'Until A, B' means "If A, not B" (B will occur until A. When A happens, B will cease)
'Unless A, B' means "If not A, B", which is just the contra-positive (Google it) of "If A, not B". They mean the same thing.
To illustrate, say that you absolutely need coffee to wake up in the morning. You could say that "Until I get some coffee, I will stay asleep". You could equivalently say "unless I get some coffee, I will stay asleep".
Grammatically, they can be used interchangeably; but logically they represent two different (but logically equivalent) conditional statements (i.e. if statements).
until is used to show ones focus on achieving a task in spite of obstacles laid along d way just making sure that the person achieves it, while unless is used to refer to making options.choosing between a thing
a sentence would be "I wont do my homework until I eat my dinner".
Don't come back until 5 pm.
She dated him until they broke up.
He had unimpaired vision until after the accident.
Example sentence - The painting appeared dimensional until you looked closer.
One possible sentence: The mixture was blended until it had a homogeneous consistency.
this sentence is going to be continueing forever until i decide to end it.
the rain doesn't start until the night.
The lion was untamed until it settled down
It hadn't occurred to me until just now.
Example sentence - The words in the book looked blurred until I cleaned my glasses.
Until now, the comet had been unobserved for centuries.
These 2 people were unacquainted until they met in a party.