I know this is stupid but I'm confused as to how to get these to work.
Could you make a tutorial or something, I'd greatly appreciate it.

ok thanks :) i figured it out

The game cache mod folder is any mod folder under the game folder that SFM knows about. For example, usermod. or if you have a special folder that you use for your matfixes and you've added that to the gameinfo.txt file above the tf folder reference in that path. For example I have a MOD Folder under game called TFMatFix. I used the "Edit search path for existing mod" function of the SDK to move it above the TF folder I would put this mat in the path Sourcefilmmaker\game\TFMatFix\materialsmodels\workshop\player\items\pyro\invasion_a_head_full_of_hot_air .

i cannot find it

where is the gamecachemodfolder folder thingy?

My model had some transparency so I'll put my fix here just in case.
Add "$ambientocclusion" "0" to both invasion_a_head_of_hot_air.vmt and invasion_a_head_of_hot_air_blue.vmt.