Bank transfer, paypal or cash on collection - it's up to the seller to specify. You advertise the item (with photos), then once a deal is agreed in the thread, you go to private message and discuss specifics (exchange personal info, bank details etc).
Be warned though, if you're new then you'll be expected to build up your trustworthiness/feedback. If you have no previous sales or purchases on there and you sell something high value (like an iPhone), high feedback/established members will likely insist you send them the phone first and then they pay you when they receive it. This isn't a bad thing and completely acceptable as trust goes both ways (e.g. someone could send money to someone and the seller not send the item).
I've sold lots of things on there, never had any problems and buyers are usually people with decent feedback.