That can be counted.
Pen, Boy, Book, Hair, Star, Girl, Man, Cow, City, Paper etc.
That can't be counted.
Milk, Sugar, Honesty, Delhi, Money, Love, Hate etc.
You must be thinking that ‘Hair’ and ‘Star’ are not possible to count. In fact, counting them is difficult because they are huge in numbers but it’s not impossible to count them; we can count them like 1 star, 2 stars, 3 stars, 1 hair, 2 hairs, 3 hairs etc. That’s why they are called countable nouns. Secondly, ‘Money’ is an English word which is considered to be an uncountable noun because we can’t say “I have 1 money, 2 money, 3 money etc” so can’t count it in numbers.