The word Jews derives from the word Judah, which was one of the twelve tribes of Israel. (Israel, one of the Patriachs of Judaism, had twelve sons; it is from these sons that the twelve tribes were named.) Sometimes they were called people of the Kingdom of Judah.
Jews have faith in One God, they follow what is called the Old Testament (they call it Tanach, or the Hebrew Bible) and they have their own prayers and ways of worship. Their day of worship is called Shabbat, (sabbath) which is a Saturday.