First, make sure your name is registered with NickServ. When you are, and you're identified, simply .. join the channel! Type /join #blabla, where you replace blabla with your channel name. The # is obligatory.

If you are in the channel, it's unregistered and you're an operator in there, type /msg ChanServ register #blabla password description. Password should be your secret channel owner password, which you don't give to anyone, and description is a short description.

It is now registered under your name, and ChanServ will automatically join. You can now /msg ChanServ help and see all the ChanServ options to customize your channel, take special notice of the SET option. Congratulations, you have made your own channel, and it's registered !