On your turn, you have two choices, you can take or sell a card.
If you take a card, you must choose between the camels, take a card from the market, or exchange two to five cards between the market and your hand.
If you sell cards, you can only sell one type of good per turn, and you receive as many tokens for that good as you sell cards. Token values decrease as the game progresses, so you need to hurry! On the other hand, you receive better rewards if you sell 3,4 or 5 cards of the same good in one sale, so you should wait!
You cannot sell camels, but they are capital to trade and they have a certain value at the end of a round, sometimes enough to guarantee you a victory! So you need to use them wisely.