As an example, I took a quick look at the Easy PBR website codeofart.gumroad.com/l/EasyPBR and the instructions are there on how to use it.  I think you mean how to install the add-on.  To do this, Go to Edit, Select Preferences, select Add-Ons, on the right top corner of the add-ons manu there is a down-pointing arrowhead, click that.  Hit Install From Disk, go to the downloaded file and let Blender3D do the rest.   Is this the method you needed to know about ?  Sorry if it is not, becuase it was hard to understand exactly what you were asking.

Eternal Hobbyist