AAAWWUUBBIS is an acronym to remember the most common subordinating conjunctions: Although, After, As, While, When, Until, Because, Before, If, and Since. If a clause begins with an AAAWWUUBBIS word (subordinating conjunction), it becomes a dependent clause.
For example:
I went to the store.
(Independent clause. This is a complete sentence.)
When I went to the store...
(Dependent clause. This is not complete without a comma and an independent clause.)
When I went to the store, I saw my friend.
(Dependent clause + comma + independent clause. This is again a complete sentence.)