If I understand what your requesting, you want to do an auto join for the channel you frequently use so you don't have to do a manual "/join channel". If so, go to Tools, Options. On the left side in the "Category" field, under the heading "Connect", click "options". Click the "perform" button and in the "Perform commands" box (if there is already something there you will want to hit enter and start a new line. If nothing is there, put the following on the very first line:
Make sure you enter that exactly, replacing "ChannelName" with your specific channel, then hit the "ok" button. (if you have multiple channels you wish to join, you can create a new command line for each channel. There may be a way to auto join multiple channels with one command but I'm not familiar with that command.
If you also want to use the auto join feature which is quite handy, create a new line in the same "Perform commands" box and type this:
/msg nickserv identify YourPassword
Make sure to replace "YourPassword" with the actual password you created when setting up your nickname.
Also, make sure the "Enable perform on connect" is check marked & hit enter.