Using Hyperlobby.......?

[SEE]

Sorry if this sounds a dumb question but how do you send messages to other players in a game? I had flyers say hello and ask me qusestion (which appeared at the top of my screen) but didn't know how to respond.

I also noticed in the briefings mention of using a camera to see the target area (to aid recce) but that also confused me (unless I have misunderstood its purpose). Many thanks as I am completeley new to MP and HL....