there is a big difference in the belief wich is pure monotheism, according to quran muslim reject evry worship associated to other than god, this is the pure politheism
the main difference between christianity and islam is that christians humanize god and deify jesus but muslims consider that god must never be compared to humans because we cannot compare him, even we cannot immagine him, he is unlike evrything, so muslims believe in jesus like aprophet of god and not a son of god or god
muslims believe in bible, also christians believe in bible but dont believe in quran,
bible considered by muslims corrupted by hands of man and made in it many contradictions and confusions so for this reason god abrogated bible and sent down a new book called quran
and many others details but this is the main difference,
but if you study two books you are going to find out that the two books come from the same source, but one of the two books is right and the second must be rejected because god is one and doesnt contradict himself
we must study two books to know truth