Level up until your higher. At your level theres no real point to grinding gold. Once you get a few more levels you should be able to run an Instance or farm higher level humanoids.
Level 13 is a bit too low to really be worried about grinding gold.
Yeah, until you're in your mid 20s, gear and gold isn't extremely important. Equip the greens you need to that drop while questing, sell the ones you don't need. Always make sure you're working towards a quest objective too...grinding at that low of a level doesn't accomplish much...leave the grinding to the upper levels.
Yeah, gold at that level won't really matter, but if you really really want gold, get Mining, and mine for a few hours, in some realms u can sell a stack of Copper for 1g , especially in Durotar