How should scientist set up the control group

When I scientist is setting up a control group they should get a product alike but really shouldn't do anything. The control group is the group that stays the same so the scientist can see what changed. So for example: if u r testing that is a dog gets more pets they will be happier. So the control group would be the dogs that have gotten the amount of pets they had before, and the other group would be the group that got MORE pets. I hope this answers ur question