There are several options open to you.
-General Buyers Market. You can move your resources to San Gallen in the Descarte system where the GBM (General Buyers Market) is located. There you can talk to the NPC Harry Wilder who will show you the contracts captains have placed. All these contracts can be filled by you with the resources you have stored in the commercial storage of San Gallen.
-Player Market. You can sell your resources on the Player Market (PM). Player Markets are available on several locations. When you store your resources in the commercial storage of a PM holding planet/settlement you can sell your resources to the PM. You do this by entering the commercial storage and using the option to sell a certain resource to the PM. Mind you that the price you attach is not per unit but for the total amount of resources you have entered!
-Trading. You can sell your resources to a particular captain. In the forums, ingame buy/sell forum (right drop down menu) or in IRC chat you can easily find captains looking to buy resources. You can trade your resources with a captain by entering the commercial storage which holds your resources. There you will find the trade option. You can be paid by attaching a price to the tradegoods or by using shipmail (the buying captain sends you a mail containing credits).
-Commodities Market. You can sell your resources to a commodities market. Normally this is Joes supplies, but in Verec-Per its TDK Emporium. Entering the commodities market you can sell all your cargo (what you have onboard your ship). Mind you that selling to the commodities market often means you're getting underpaid!