in writing/reading, what is 2nd person and 3rd person?

2nd person is the pronoun covered by "you"

3rd person is the pronoun covered by "he" "she" "it" "they" "them"

first person is about ME telling you about ME
second person is about ME talking to YOU
third person is about ME talking to YOU about HIM

in first, there is just one involved
in second, there are two of us
in third, we are dealing with three