It‘s just sitting there in my backpackdo i sell it? is that it?
You can auction it (which will get you more money than you would get just selling it to a vendor), or if you have another profession that uses copper (like blacksmithing or engineering), you can use it for that.
If you have blacksmithing (or another profession that uses it,such as engineering or jewelcrafting),then you can use it to make armor,weapons etc. If you don't however then yes,all you can do is sell it. I wouldn't sell it straight to a vendor though,but instead on the auction house.