I was wondering how to add breakable glass (like it breaks when you shoot it or from grenades, etc..) to a map I'm working on. That, and where to get the tags for it.

Read the HEK tutorial it says it there. Hint: http://hce.halomaps.org/hek/index.html?start=references/general/materials_overview.html

In the material name of the glass, put - at the end of it. For example if your material as called glass, you would put ''glass-'' (no quotations).