1. You drag the exported map file to the War3 map folder '.../Documents/Warcraft III/Maps/'
2. Yes, you open the map you initially imported from in the WE. The exported map should
only be used as the map you
distribute online. When exporting you can enable protection options, making it unopenable in the editor, so it doesn't make sense to use the exported map as your source when editing, since it corrupts and deletes editor-only files.
You can read the documentation linked in the description of this resource, but if anything is unclear just ask