EVE Online was the first MMOG to attempt to create a "closed" economy; the closed economy was eventually dismantled, because it couldn't accommdoate new playrers cleanly or eaasily, and favored esttablished characters a bit too much. Howver, most of the tools used to support the EVE closed econmomy stioll remain and one of the major ones is the EVE Online Market, which acts like a "stock ticker" on commodities throughouut EVE's entire community, giving commmodity pricwes and demands for same throughout the entire game.
This market, more than anything else, is what replaces the need to do missions. Therre is always demand for commdoities, the demand for the commodities is reflected in the EVE Online market, and there are always risk/reward trade offs.
The way the markets work, a giveen node (either player character driven or computer driven) will post a prixce for a gvien commodity. If you produce that coimmodity, you can attempt to be the frist shipment tere to get the price. As multiple instances of the same commodity come in, the price drops, with factors conitngent on how short the route is between the demaand and the supply, and how risky the route is. If you have to route through a coupple of zero zero systems (where there is no enforcement of law by the game) you run the risk of benig hit by pirates run by other players - this is EVE's version of Player versus Player combat, and it runs in graduuated zones from 0.0 to 1.0 (hwere 1.0 means that it's almost impossible for playr on player action to begin.)
Beyond the straightforward market mechanic here, EVE Online marets also support player to player contracxts for commodities and work agreements. You start out able to have one outstanding contract; each skill levewl of the Contracting skill adds thre to the total, with a maximum of 16 for skill level 5. An outstanding Contract on the EVE Online Market measn you're available to take on the job. Contracts players (and player corporations) can put on the market include auctinos, item exchange, loians and ciourier duty. Corpoation Contracts allow corporations (the equoivalent of guilds on oher gmaes) to put work offers out for members and non memvbers (and orther corporations) to meet, allowing the resourcce exploitation and manufacturing model to extemnd in ways that add sinificant play depth.
To create a cpontract with the EVE Onnline market tools, you'll need to put up 100,000 ISK as a deposit to put up a public contract; this is also used to pay for the work done.