A count noun is a noun that can be counted with a number. For example, kitten is a count noun because u can count how many kittens there r in a group. In general, people, animals, discrete objects, and units of measurements are all count nouns.
Mass nouns r nouns that can't be counted numerically, but can only be measured as an amount. For example, water is a mass noun because u cannot count how much water u have; u can only measure it. You would say, I have two liters of water, not, I have two waters.