The subject of a verb is the person or thing performing the
verb.
Examples:
Thecat ate the porridge. ("The cat" - subject of the
verb "to eat") Alan
complained about his new job after an hour. ("Alan" - subject of the verb
"to complain") I am
not guilty. ("I" - subject of the verb
"to be" (i.e. "am"))
Who
was that? ("Who" - subject of the verb
"to be" (in the past tense; i.e. "was"))
Interactive example:
My wife and I
appreciate all the support over the past month.
[show me the subject]