Channel linking allows you to send users who attempt to join #oldchannel into #newchannel. This is useful when you have created a new channel and would rather the users be sent there. (#oldchannel will be the initial channel with the users. #newchannel will be the channel in which you want your channel to be forwarded to.)
First, you want to forward your channel to the new channel:
/mode #oldchannel +lL 1 #newchannel
To set this permanently, you will set a mode lock on your channel (suggested!):
/cs set #oldchannel mlock +ntlL 1 #newchannel
Setting "+l 1" changes the user limit in the channel to 1 (this can not be set to 0). Setting "+L #newchannel" sets the channel link to the #newchannel whenever the channel limit is reached (which would be 1). In order to set +L, you need to be a channel owner (chmode q).
Second, you need to accept the link in #newchannel from #oldchannel.
/mode #newchannel +I ~L:#oldchannel
This sets an invex for ~L:#oldchannel, which allows #oldchannel to be forwarded to #newchannel. Without this, the channel link will not be successful.