MRSA is a Staph infection that is resistant to some antibiotics (including methicillin, oxacillin, peicillin, and amoxicillin). MRSA is either hostial acquired (HA), meaning you caught the bacteria during a stay in the hospital, or community acquired (CA), meaning you got the bacteria somewheres else (most commonly a gym).
Many people who get MRSA are healthy individuals who are going about their normal lives. It is contagious by touch only. The gym is often a source for MRSA because people leave sweat behind on the equipment. You can also get it from towels, sheet, clothes, etc. that are contaminated. MRSA is usually transmitted by the following pathway:
Infected person contaminates object, you use object, you get bacteria on your hands, inadvertently you touch your nose, the bacteria enter your nasal canal, the bacteria colonize in nasal canal (often leaving sores in nostrils), bacteria stay on you for a while and finally present themselves as a skin infection.
On the other hand there are some people who are carriers. These people have the Staph bacteria colonized in their nose, but never present any type of infection. You can still catch Staph from these a carrier.
MRSA will usually present itself as an infection of the skin, such as a boil. A boil looks like an enlarged pimple and is filled with pus. You can get boils anywhere on your body and if untreated they can grow to be very large and endanger your life. See advice on treating MRSA Staph Infections.