EVE’s market is mostly player-driven, which means you’re not buying from a magical NPC store. You’re buying from other capsuleers, in specific stations, in specific regions. When you open the Market, you’re basically looking at a list of sell orders (people offering items for ISK) and buy orders (people offering ISK for items). The market also shows price history and volume so you can tell whether you’re about to overpay for something that no one actually trades.
EVE’s market is player-run, so you’re basically shopping off other people’s listings, not some magical NPC store. You’ll mainly deal with sell orders (pay now, get item now) and buy orders (set a price, wait for someone to sell into it). Buying from a sell order is instant but usually pricier; placing a buy order can save ISK but takes time. Selling works the same way in reverse: selling into a buy order is instant cash, while creating a sell order usually pays better but you’re competing with everyone else.
The easiest way to embarrass yourself on the market is location. Items don’t teleport. If you buy something that’s listed 10 jumps away, congrats, it’s now your problem 10 jumps away. Always check the station and number of jumps before you click “Buy,” especially when you’re rushing fittings or doing bulk purchases. If you’re trying to be smart about pricing, use the market’s price history and volume to see if the price is normal and whether the item actually moves, because a “good deal” is useless if nobody buys it.
Most market pain comes from people not reading the details: buying in the wrong station, ignoring minimum-volume requirements on buy orders, or assuming the highest price means “best option” without checking where it is and what strings are attached. For Starfleet use: use the Market for standard modules, ammo, and quick replacements, and use Contracts for fitted doctrine ships, bundles, and internal corp distribution so everyone gets the exact right stuff with less chaos and fewer “wait which fit?” messages.