if I remember correct upon entering the FP you get the message that 2 players are recommended.
You do, it pops up something like "A group of two players is recommended" in red letters in the middle of the screen when you enter. That would be pretty easy to miss though if you were looking at a menu at the time (character sheet, log, w/e).
But yes, it also says [GROUP 2] in the mission name
You're supposed to do it with three others, use the button in the top left corner of your minimap. That is the group finder and should select the Flash Point's you are eligible for. Just join the queue and wait for it to pop. Make sure your selected role is highlighted be it for Damage per second, Tank, or Healer.
Group Finder for Black Talon is actually kinda silly. It's not designed for four players like the rest of the flashpoints, it's intended for two. It's silly to wait specifically for a "tank + heal + 2 dps" group to be put together, when it isn't needed or even really meaningful, as at lvl 10 tanks can barely tank and healers have like one healing ability. Easier for BT to just ask in chat if someone wants to do it with you (and less time-consuming for a dps than waiting for group finder
@OP, just for future reference, if a mission-giver is going to give you a flashpoint, you can tell in advance because it says "flashpoint courier" under the NPC's name when you hover your mouse over him. That way if you don't actually want to do a flashpoint at that moment, you don't waste your time sitting through the dialogue just to get a mission that you don't even want.