In AmE, to "hook someone up" is a slang phrase that is normally used when someone is connecting with another, usually supplying a service to someone, often something illegal or bad.
"Hey, Tom, can you hook me up with your brother who fixes cars?"
It can be used for the transaction as well, like "I met with Fred and he hooked me up with some weed."
"To hook up" can refer to casual sexual encounters. Like "I went out on Saturday night and hooked up with this girl, but i don't think I'll ever call her."