In case you're not familiar, IRC stands for Internet Relay Chat, which is a protocol for exchanging messages. IRC is mainly used for group discussions.
A number of Vim core developers and users frequent the Vim IRC channel. At the moment of writing the #vim IRC channel on freenode.net averaged at a 1,000 users a day (not all active at once of course, as IRC has many idlers). The Vim channel is a great place to ask questions and get a general feeling for the Vim community.
You can log in through the Freenode's Web client at https://webchat.freenode.net or through an IRC client of your choice. Personally, I prefer using the irssi command-line client, but it takes quite a lot of tinkering to get the settings just right.