could anyone tell me or link an old thread for a beginners guide please ...making caster / melee channel commands etc.

That's a pretty open ended request. Could you be more specific?

without being more specific, we can just direct you to the documentation. The commands basically work like normal eq commands, /sit, /camp, etc. different plugins add different commands. There are infinite combinations of what you can do so without a specific request it's hard to answer. To learn more about the commands and other tools:

mq2melee documentation for how to format melee commands
mq2cast documentation for how to format cast commands
mq2eqbc/eqbcserver documentation for how to send those fancy commands to other remote characters
mq2netbots documentation for how to share/access character information over mq2eqbc