Meaning for sentence 1 and 3: To have sex with someone you are not in a relationship with. Similar meaning to "one night stand". The meaning in sentence 2 is similar to "help me if you are able" For your sentence, it would be something like "if you know a good person, help me by and introducing us." It is making a request for something.

Helo, i'm new here! How are you ?

Hi Mina! Hook-Up is an informal phrase. It means ,meet or form a relationship.