Attend your first weekly meeting.
Virtually every Mozilla project has a weekly (or bi-weekly) meeting that contributors call into using a telephone, voice or video chat.
Find out the date and time of at least one meeting you're interested in attending. Then, obtain any required software or equipment for calling into the meeting, and schedule a practice call with a peer. If your meeting has a dial-in number to a conference room, for instance, try calling into the conference room a day before the call.
Practice muting and un-muting yourself to ensure that you can participate in the meeting without echoing or exposing the other participants to background noise on your side. You may want to consider obtaining a good headset if you don't have one already, as using your computer's built-in mic and speakers often causes echo feedback.
if you have trouble, feel free to ask for help here or in #newbies!