First see
How To Register Your Nickname. Your nickname must be registered, and you must have executed the "identify" command before registering a channel.
First you must "join" the channel to register it, and it must be free to register (it can't belong to someone else). The command is:
/join #channame
Where #channame is the name of the channel (example: #chatplace)
Once you have joined the channel, type:
/cs register #channame *password* *description*
Where #channame is the name of the channel (see above), *password* is a password of your choice, and *description* is a short description of the channel's purpose or theme.
In order to make changes to the channel (such as setting modes or topic) you must be "identified" to cs:
/cs identify #channame *password*
Where *password* is the same password you used to register the channel.
You will have to "identify" to cs every time you enter the channel, if you intend to make changes. If your IRC client has the ability to perform commands on connect, placing the identify command in its perform section means you won't have to do it by hand.