Question

In tasks I can guess which to use but I don't really get their meaning.

Answer 1

Firstly there is no any similarities between them.

We use UNLESS when we don't want to say İF NOT.(I m expecting you've already known that)

We use UNTIL when we would like to say a  not before a particular time or event.(or as far as)

Examples:

 He waited until(or shortly till) she was finished talking.

You may not get this job unless(if not) you've got experience.

Answer 2

The difference btn unless and until that unless expresses condition eg:you will lose unless you train well. But the term" until"express time eg:we can't begin study until you calm down.