new, questions regarding fire teams and PS4

Borderlands did it all for me, it comes up with a list of people playing grouped by level, you make one click and send an in game invite is sent to the person, they presses join and you are ready to go in with Mics available. my problem is None of my other friends are playing destiny. I do not want to find a chatter box but it would be nice to know where they are going, how long they have to play and discuss a little strategy Can someone go through a stepped process to explain how fire teams relate to Clans and groups? I got an in game invite, never met the dude. played but there is no record who you played with or how to message or request friend. How do you join or start fire teams. Is the chat just in for teams with Mics in a fire team or group on the same platform? I keep odd hours, one day is it late am hours, the daylight or after noon and occasional evenings seems this system makes it hard to play together or at least a little confusing. Thanks Ross