First, you need to know that there are many different networks. A channel on one network may not be on another network and even if it is, it won't really be the same channel. So the first step is to know what network you want to connect to. If you just want to try chatting and don't care what network you are on, you can choose one of the networks in mIRC's server list under options.
Once you have connected to a network, you will normally just have a status window and won't be in a channel. Some networks will automatically force you to join a channel, but most will not. To join a channel, type /join #channelname (replace #channelname with the name of the channel). You can join any channel even if it doesn't exist, so if you join a channel without anyone in it, then it probably isn't a channel that existed before you joined it. If you want to find other people to talk to, you will want to join a channel that does exist. To get started, most networks have a #help channel that you could join (/join #help) to ask questions and verify that you can see people. You can also see a list of channels that have people in them by typing /list. Then you can join a channel that is in the list and you should see people there.
