Using the material pack is super easy:
- Unzip the "MAIN.zip" file into a new folder.
- Download all the other zip files you have purchased from BlenderMarket and extract their contents into the MAIN folder.
- If you have bought all 4 materials then the folder should look like the image below.
- You can now append the materials into any other .blend file. Simply open you destination file and go to "File", "Append". Then navigate to the file you bought from BlenderMarket to import its materials into your scene.