What's the difference between a noun and a pronoun?

Nouns and pronouns are very similar, so be careful not to get them confused!

A noun is an object or a thing, for example:
'The cat is sleeping.'
Here the noun in the sentence is cat. You can often spot a noun because it is 'doing' something. In this sentence the cat is sleeping. 

Examples of other nouns: box, house, machine, airport. 

A pronoun is used to replace a noun in a sentence. The both have the same function. 

'The cat is sleeping. He is dreaming about fish.'

In this sentence the pronoun is 'He'. We know that 'He' is referring to the cat. A pronoun has been used to avoid repeating 'The cat is...' In this case, using a pronoun also gives us more information about the cat, we now know it is a male cat. 

Examples of other pronouns: she, they, it, who, some, this.