first congrats on turning 21.
next, get some training on paper (some sort of documentation) take a CCW/CHP class. (even though MD is a hard state to get a concealed permit from) Then goto any local gun dealer and try out how different guns feel and fit in your hands, look for something comfortable.
after that make sure you have all documentation needed to obtain/purchase the firearm.
then search, there are deals out there. someones always looking to sell as well as someone is always looking to buy.
My parents are right in A.A. CO, let me know if you need help searching for some places to buy.
DPMS Low Pro Classic (multi-cal)- .22LR/.223/5.56
Winchester 1300 - 12Gauge
Glock 23 - .40S&W
Charter Arms - .38SPL