Answer:
Essentially you go to a recording studio to record. When it comes to bands recording music, most studios will also mix the record and some will also master. You can find studios that specifically mix, and master as well.
Obviously a recording studio will "record". What it records is really up to whoever books time. Generally its musicians recording music. But they are not limited to just music. Voice dialog is also recorded at studios. Whether its for a local independent movie, or a radio commercial it can easily be done in a recording studio.
Another feature studios can offer is being able to make dubs of things. When I worked at a studio we had a little frail old lady come in with really really old reel to reel tapes of a church choir. She wanted us to make cd's of those reels so they could continue to be enjoyed. Because studios have tape machines and other odd pieces, they can often be used to make better copies of existing material. As a side note, those recordings that lady had were amazing.
Because of the way the music industry is going, a lot of studios are branching out and doing more than just recording. A lot of labels are forming around a studio. This saves the label money by being able to record without having to pay someone else to record their bands. Also you can probably find studios that do more with the manufacturing and duplication of cd's. So not only do you record your music, you also get your cd's printed up with them.