What is the difference between すみませんが and すみません? I'm still a beginner with japanese. Here is the example that I foud: I'm not completely sure about the meaning of in this sentence, since the teacher told me you can both use it or not. What is it for?

simply means "but".

> **** =
>
> "Excuse me, _**but**_ please pass me the sugar."

You can also make the same request without using by saying:

> =
>
> "Excuse me. Please pass me the sugar."

The difference between the two is almost too subtle to mention. It just flows a little better with IMHO.