Any hope of a training game?

I've signed up on RPGGeek to run a couple of games in Virtuacon in October, which will use Google+ Hangouts and Roll20. Problem is I have little to no experience on either of these platforms (I have a Roll20 account but have never used it to game). I need training, and practice, if I want to get up to speed by October. Does anyone have a suggestion?

when is virtuacon and how do you join

<a href="http://rpggeek.com/thread/955812/rpg-geek-virtuacon-13-organizers-needed" rel="nofollow">http://rpggeek.com/thread/955812/rpg-geek-virtuacon-13-organizers-needed</a>

Perhaps more to the point is this recruiting thread for potential gamemasters. It covers, among other things, the time-slots and the other preferences, and people are volunteering on the thread.. I have a problem -- I scheduled my Doctor Who Adventures in Time and Space game at a time that works well for me in Oregon, but is dreadful for British players who would probably be the most interested in playing in the entire lot. So I'm really hoping someone steps forward to run a UK-friendly Doctor Who session. <a href="http://rpggeek.com/thread/972653/virtuacon-2013-gms-needed" rel="nofollow">http://rpggeek.com/thread/972653/virtuacon-2013-gms-needed</a> GMs have until mid-July to sign up. Players can start signing up for slots in early September. The event is October 18th-20th. There are no plans to charge admission.