does vs is and (did + present)

[Ahm992]

hello teacher,
i have a question i dont know how to compar between does and is
for example:
why i use is here
He is a doctor
not
He does a doctor

the second question:
yseterday i recived an e-mail which it contain this sentinces
did you find.....
why we use find(present) not ( found)
after did(past)????

thank you

[Kitosdad]

He is a doctor ..... third person singular. That's how it works.
_________________
Keep it simple ... Keep it interesting.