Here's how to join:
First of all, open up your IRC client, and poke around a bit. Don't touch anything, but look through the options and get familiarized with the program. Once you think you know what you're doing, connect to Thinstack (if you can't find out where to do it, just type "/server irc.thinstack.net" and press enter), once you're connected, choose your nickname. If you didn't choose it in the options, type "/nick [yournickname]" (just your name, no brackets or quotes necessary. IRC only uses letters, numbers, and the dash, underscore, tilde, and graves as acceptable characters for nicks, no spaces).
You'll know if the nick you chose is already used, if someone's already using it, or if you get a message saying it's already registered. If this happens, just choose another one. Next, all you have to do type "/join #channel", and you're in!
That should be it! If you follow those steps it should be fine, and hopefully there shouldn't be that much trouble. Have fun in IRC!