The OP stated that (s)he couldn't find how the Perform section operates, not the Scripting section.
The Perform section is located in mIRC Options -> Options -> Perform
Using /help perform brought beck the little bit of help that's in the help file for this area. It's not much, and then refers you to the Aliases section. This is one (of a few) reasons why I prefer and recommend the scripted version.
