Hi kcliff01.
At the top of this forum is an Announcement with information on equipment:
http://apneasupport.org/viewtopic.php?t=6732
Inside that announcement, is a multimedia gallery link for machines and masks. Please have a look, a number of the mask interfaces are detailed there.
In brief, there are only a few types of masks:
Nasal cushion ("cup") - the traditional looking mask that fits over the nose
Nasal pillows - these rest up against the nostrils to form a seal but do NOT go up inside the nose
Nasal directseal - a variant of nasal pillows that has a different shape, works better for some people
Nasal prongs - there are only a few makes of these, they DO go inside the nose to form the seal
Full face mask - one piece that covers nose and mouth
Hybrid type full face mask - combination of mouth coverage + nasal pillows
Mouth-only mask - this leaves the nose free and covers only the mouth
(I don't think I missed any...?)
People who mouth-breathe usually end up with one of the last three, though some people who mouth breathe have success using a nasal mask, a chin strap, and sealing their lips with gel or tape. And some people have been able to 'retrain' themselves to not breathe through their mouths at all.
Some folk don't mouth breathe but the CPAP air manages to find its way out from under the lips. I'm one of those, I have a full face mask simply because it is more comfortable to me than sealing my lips. Air lost other than through the exhaust vents in the mask, is usually responsible for a decreased effectiveness of your CPAP therapy.
A nasal mask is fine if mouth-breathing or lip leakage is not an issue. Many people like the pillows type of masks, if their pressure isn't very high (below 15 or so, depends on the mask). Pillows masks and some nasal cushion masks are only rated to a certain maximum, and will misbehave at higher pressures.
Again please have a look around the information available at the top of this (and the other forums), many of your questions will be answered all at once
Blessings,
--pseudonym