"мой знакомый есть большой дом?"
In this case "есть" is "is".
"My freiend is big houst" is incorrect of course.
Obviously you mean "имеет" (to have):
"Мой знакомый имеет большой дом" is ok.
In russian "У X есть Y" can be translated as "X has Y" in some cases + "is" can be omitted. Grammatical cases mean a lot. Literally this pattern can be translated more directly as "There IS Y (somewhere) belonging X". "is->есть", "belonging->у". This is why you see "есть(is)" in this sort of russian phrases.