Hi @Kelvin1
Those are different levels of permissions eg: files.read will give the read only permission on the aharepoint document library files.
Site.write will give the permissions on the site leve that is to all libraries , lists and other compnents on aite to be editable
For any run to use graph api you have to enable the required permissions so that you can access those reaoirces using geaph api
Cheers