Split Keys: Shape Key Management
Is this addon present in Shape Key Collections or Master Shape Keys?
Yes, but you'll have to check them out to see in which variant.
How do I activate an addon?
Use this 20 sec guide - https://youtu.be/wOv4oHO5Kqg
The .zip doesn't install in Blender
Please un-zip the archive and install the .py script.
Are there tutorials?
Of course, check the Documentation section of this page.