Just obey the instructions. If Scratch variables changing several times a second is a problem for you please don't use this project.
NB If you're still 'New to Scratch' you can't use cloud variables so this won't work for you.
This demo doesn't actually use cloud variables because if it did and the project was already running elsewhere when you start running it that would give confusing values. What's important here is the idea, not the actual use of the cloud within the demo.
Many people in the help forum seem to need help with multiplayer and I have a demo elsewhere but this is more basic and just shows one general method. Once you understand the method it is relatively easy to implement and expand to meet your needs.
Multiplayer doesn't have to be difficult!
This is used in https://scratch.mit.edu/projects/63501310/