The second way is loot. Knowing about everything in game that enemies drop after killed is useful to someone.

This is a big change from other MMOs where the loot that the enemies leave behind is mostly trash to be dumped off at the nearest NPC vendor. Because just about everything you will find is in demand somewhat, it makes liquidating the items you found a bit more challenging if you want to get the best price.
Once you have obtained a piece of loot, you can check the market screen to see how much it is worth. When looking at the "Sell" section of the market screen, you will see that some of the items in that list are highlighted green. The green orders are the ones that can be filled in your current location. For instance someone might be buying Foxfire Rockets for 100 Eve Isk 2 jumps away, but they are only paying that price if you are in that system so that order will be listed without a green highlight. Now you must decide whether you want to fly over 2 jumps to and sell your rockets for 100 Eve Isk, or stay in your current system and sell them to someone who is offering less than 100 ISK.