Collectors, also known as Collector NPCs, are NPCs at solar system space stations (as of this page being written, the only one is at Exator Station, located on the outskirts Sobrii). They allow the selling and buying of certain items and reward you with credits and SLXP. While they might not be the best way to get SLXP for high level players, they are great for players between 1 and 11.
As a new player, the first thing you will want to do is know where you are selling to. As of this page being written, everyone will sell to Exator, however there may be other options in the future. The stations buy by the stack and can only buy so much per day. To sell, right-click the collector. To buy, left-click them. The buyable items go as followed:
Note: You can not use ships bigger than what you could fly yourself to transport items.