Countable nouns are easy to recognize. They are things that we can count. For example ‘apple’
We can count apples, we can have one, two, three or more apples.
When a countable noun is singular, you have to use a word such as:
a or an/the/my/this.
You will notice that if you do not do this, the sentence sounds incorrect.
I want an orange vs I want orange