In Modex, there are three tabs: Resoources, Elements & Files
First: 'Files' is the place where to put javascript, css & images. I also want to put font, but it doesn't allow me to upload. Maybe upload fonts by SSH could be possible.
Resources is the place to put html files.
Each html file is called 'document' in MODX.
'Elemets' is such more important. All MODX's good stuffs are located here.