First you have to take a GMAT exam and once you have the score you will have to apply to different universities (very easy to do online now) until you get accepted somewhere, or in several. It is very easy to get all the info you are looking for on the internet. Simply type GMAT and you will get access to all kind of info.
Some good schools in Washington DC metropolitan area:
George Washington University George Mason University University of Maryland
I have heard that on-line Universities don't require the GMAT to have an online course (much much cheaper than going to the States, and they are internationally recognized), you only have to be proficient in English and to be able to read and understand written English. in google you can get some addresses type: online MBA course... and good luck