The history of the Jewish people and of Judaism stretches back 5,774 years. To answer your question, start here and keep reading:
Judaism is the word used to describe the religion of the descendants of Abraham, through his son Isaac and his grandson Jacob. Abraham lived about 4,000 years ago and he had eight sons, but his Covenant with God and his inheritance of land was given to Isaac. The Covenant is a binding, perpetual contract with obligations.
When Jacob fathered twelve sons, God changed his name to 'Israel.' Thus, the twelve sons became known as the 'Children of Israel' and their descendants became the 'Twelve Tribes of Israel.' Judah was one of those tribes. The word 'Jew' comes from his name and is the pronunciation used by foreigners, because there is no 'J' sound in the Hebrew language. In Hebrew, the word 'Judah' is 'Yehuda.'
The religion of the Tribes of Israel is the worship of only one god (one of the 'elohim') and the observance of the Covenant He requires of them. It is impossible to transliterate or to define the name of this god into any other language. In the Hebrew it is:
The worship of the God of Israel is open to all people and He promises: "You will find Him if you search for Him with all your heart and all your soul." (Deuteronomy 4:29) "If you seek Him, He will let you find Him." (I Chronicles 28:9)