There's not a particular place you can learn to script. However, many say to start at Aliases. Type /help Aliases
in mIRC. Popups are quite easy to learn too. You may wish to see /help popup menus
and /help Remote Scripts
On top of the relatively simple help file (it's a better reference than teacher), you can use many websites which have been started up by users of mIRC whereby people have submitted their own scripting tutorials. Such sites include www.mirc.net
- click on the 'Tutorials' section.
..And on top of that, just plain experience helps a heck of a lot