You can, of course, Create a new campaign & invite people into it, for testing, practice, Q&A, learn the dice roller, etc. That would generate a chatroom in which you can invite anyone who is on this site. Of course you would need to find the new folks & get them into your campaign to chat with them, it wouldn't be just open to anyone who stumbles by looking for chat help. A possible name for a Roll20 campaign that is open for teaching is a "Tavern", and there are a few Taverns already existing on Roll20 that can be found in the LFG. I created a 2E Tavern campaign which is geared towards helping people who are interested in playing AD&D 2nd Edition On Roll20. In my Tavern campaign I have helped a few people get acquainted with R20 features, as well as pitching games and finding players, connecting people. It's like a particular-game-focused subset community within the Roll20 community.