Can anyone tell what で means in this sentence: 私は学生で友だちはいしゃです。Thank you. It looks like the で in this sentence means "and" but I'm not really sure.
You are right, it means "and".
That is the te-form of the copula だ.
According to "A Dictionary of Basic Japanese Grammar", page 466:
"The te-form functions, in part, to link sentences"
Jim went to Japan and studied.
This steak is cheap and delicious.
This apartment is quiet and good.
My father is a teacher, and teaches English.