Tamp is a fancy word that means pressing down with force.
Imagine you have a bucket of sand and you need to make a sandcastle. First, you need to make the sand compact by pressing down on the sand with your hands. This is called tamping.
Another example of tamp is when you make coffee. After you put coffee grounds in a little basket, you press down on them with a special tool called a tamper. This presses the coffee grounds together and makes them ready for the hot water to go through and make delicious coffee.
So, tamp means to press down hard to make something more compact or to prepare it for a specific use.