Where exactly do i type it? or should i give it in a script?
type it anywhere in mIRC If you want to make an alias you can, if you want to , you can assign an f-key in aliases
f12 scon -atl #chan
then all you have to do is type the f12 key
also note in the channel setup you can choose to join that channel "on connect" with no scripting
select the channel in the channel dialog, click "Edit" check the "join on connect" option.