- The cat slept on the bed.
The cat is the subject of the sentence because it is sleeping. The bed is the noun.
Yes, the cat is also a noun (a person, animal, place or thing), but in breaking apart this sentence the cat becomes the subject because the sentence is about the cat doing something.
Some more examples of subjects, verbs and nouns:
- Fergal [subject] loves [verb] books [noun].
- I [subject] like to eat [verb] chocolate [noun].