Dependent clauses are independent clauses that start with a subordinating conjunction: because, if, while, before, after, when, as, since, once, whenever, whatever, as soon as, although, even though, that, which, whichever.
Subordinating conjunction + independent clause = dependent clause. They are called "dependent" clauses because they depend on the independent clause they are matched with to make sense.
A restrictive clause is a group of words that add necessary information to the sentence. If you remove the information from the sentence, it will not make sense. So, you do not place commas around restrictive clauses.
A non-restrictive clause is a group of words that add information to the sentence that is not necessary, but does add to the details of the sentence. If you remove the information from the sentence, it will still make sense. So, you do place commas around non-restrictive clauses.