Video camera not essential for a Huddle (you can join by phone) but video is definitely the way to go if possible.
There will normally be a thread posted (often Thursday sometimes Friday) on the Huddle Forum asking for those wishing to attend to register their interest.
Then (again normally Saturday morning 10ish)
@AgentPete will DM (conversations they're called here - via the little envelope icon top right of your screen) those who have registered with the login details for the conference call. Starts 5.00pm UK time and it's always a good idea to get there a little early to test your sound and vision connection. You can test from 4.30 onwards.
On that same thread (the DM) people will then attach (ideally as a word doc) whatever it is they'd like to share and discuss with the group - and it's as simple as that.
Depending on volume of submissions and how long each takes some may carry over to the following week's Huddle. Material varies from opening pages, to blurbs, synopses, titles etc. or even general questions about the industry. Anything writing, agenting or publishing-related goes pretty much.
Well worth participating as they are both very informative and good fun too.
Re Pop-ups there is a live chatroom here on Litopia during the broadcast and you can comment there. Or indeed on YouTube if you happene to be watching there. So no Twitter account necessary.
@Galadriel