Peering Exchange

If a service provider or enterprise orders collocation at an Equinix Global Internet Exchange Point, and orders a port on the exchange from Equinix, then what happens? How does a provider actually peer with the peers on the exchange? Lets assume the SP or enterprise already has an ANS, transit from multiple providers, and a BGP router that can accept and hold full routes. You can see the members of the exchange on peeringdb.com. Many of the members say their policy is Open with little to no traffic requirements. So does just ordering a port to the exchange automatically connect you with all of these open providers, or do you have to contact each on individually?