What does first person and third person mean?

1st person is from your own point of view, the person speaking.

examples:

I play football. (singular)

We play football on Saturday. (plural)

3rd person means the person or thing spoken about.

examples:

He plays football. (singular)

They play football on Saturday. (plural)

The nouns 'football' and 'Saturday' are third person nouns, the things spoken about.

Note: The 2nd person is the person spoken to. The second person pronoun is you.