Welcome to the beginning really for destiny. The best and fastest way is to run all bounties on either Crucible or Vanguard and continue to run vanguard strikes. This is very time consuming and a grind but when you get to rank 2 on either playlist vanguard/crucible you should have enough marks buy the armor from the vendors. Alternatively you can stack both bounties and reputation to a faction (FWC, Nee Monarchy, Dead Orbit) and that will make the climb shorter but also will prevent you from gaining reputation form vanguard or crucible. Also note that you we need to play crucible to spend the marks on the faction armor. If you are on Xbox 360 I offer my help to you. Also note that you can win legendary engrams from running vanguard strikes. These can give you the armor from the Cryptarch. If I was in your shoes I would run vanguard strikes to get Rare (Blue) armor with light and get to level 26 and run Vault of Glass it can give you legendary armor from beating bosses. Also note that blue engrams have a chance to turn into purple. For me it seems to be a legendary item one out of every 100. Good luck