404 errors,help

[FTG LIQUID CL]

Anytime I try to add a mod,that has extra files, I get 404 error file not found.I have no idea whats wrong.I use filezilla to add the files to the server.Where it says remote site ,I type in public_html/forum.The files appear to upload.But when I add the product xml..,and go to the pages the mods create,I always get a 404 error.I know it is because of something I am doing because I paid someone to add some files and they work just fine.Can anyone explain in detail how to upload mod files to my server using filezilla.I am very new to this so please explain it to me as if I am retarded.Thanks for your help.