The #cap-im and #cap-im-spoilers IRC channels are on DALnet. If you’re using a regular irc client the server is irc.dal.net and the channel is #cap-im and/or #cap-im-spoilers. There are three different options below of web clients. If one doesn't work try a different one.
Got to https://kiwiirc.com/client. Type in the nickname you wish to use. The channel name is #cap-im or #cap-im-spoilers. There will be a little blue link that opens up the server and network info. Click on that and enter irc.dal.net as the server and 6667 as the port. Here is an example of what it looked like when I filled it out.
Teyke found yet another web client option if the two above aren't working. Go to http://www.wsirc.com/ and fill out the box to the right like Teyke's example below.
The http://www.dal.net/ web client sometimes doesn't work, but people still have used it successfully to join the the chat. Under Chat Now fill in your nickname, and #cap-im or #cap-im-spoilers.