Nouns are just the names that we give things. The first words babies pronounce tend to be nouns: Mama, Papa, duck, bird, teddy.
The word noun comes from the Latin word nomen, meaning 'name'. See if you can work out what is meant by the following Latin proverb:
Bonum nomen bonum omen.
That proverb means 'A good name is a good omen'. Thus, Romans gave their children names such as Victor (victorious) and Valerius (valiant) or Aurelia (golden) or Vita (life). Because these are names given to people, we call them proper nouns - and we start them with capitals.