Thanks for the nice feedback 
When you buy it from the Marketplace you get a ZIP file that contains a folder “ModularMenuSystem”, which you extract into the Content folder of you project(s). Within that folder you have some sub folders and a bunch of of BP asset files. That is basically it, you extract the ZIP file and from then on you got some new BP nodes to use in your project. Simple as that
Please let me know if you need anything else.
Cheers!