Jews are descended from the tribe of Judah (Judah being one of the 12 sons of Jacob, later named "Israel"). You could also say the tribe of Benjamin, but as time went on, Jews forgot tribal distinctions altogether.
This is because, according to the Bible, Israel initially was a kingless, theocratic nation. Then, the people wanted a king, chose Saul, who was replaced by David, even though David didn't want to overthrow Saul, necessarily, and then David was succeeded by Solomon. After Solomon, it was split into to, with the lower half (and two tribes) becoming Judah and most of the rest, Israel. Israel got pogromed out of the picture at some point (arguably blended into Judah, but for the most part they were dispersed), and various Empires ruled over the Jewish homeland, most importantly Rome, who named the province Judea. Then, Christianity arose, Jesus and the Apostles went against the prevailing Jewish sects, the Jews revolted against Rome and lost hard, and eventually were dispersed away, becoming mostly minorities in other nations. Over time, the notion of Israel, Israelites, and the Jews began to blur together.