Yes, Jews practiced something that in English would be called Baptism before John the Baptist. However, there were many different groups who viewed it in different ways.
The laws for baptism (which i will henceforth call immersion) had to do with ritual purity. It's hard for us to grasp how much purity mattered to Jews/Israelites in times of yore since we no longer have a temple. But just to give a small illustration, if you were a woman, and you flipped out and stabbed someone, and they escaped but died on the road, you could still go to the temple and stand before God because while you had sinned, you were not ritually impure. But a woman on her period? She is unfit to stand before God.
The rules and laws of immersion as set forth in the Bible all had to do with purity. Whether it was contact with corpses, seminal emissions, sex, leprosy, etc etc. But after the Jews returned from captivity, you started seeing new and innovative religious innovations. People could go to Synagogue rather than the temple to learn, people were encouraged to learn to read and write for themselves, to take on small traditions that usually only the priests did (like washing ritually before eating). And there started cropping up different views of immersion, and just how certain actions could make you impure such as sex, perhaps also sins caused spiritual impurity, and therefore getting immersed could clean you of those impurities as well.
In terms of the specifics, who did what, and how long. Most of that information has been lost. But we do know that people were doing it, and for lots of different reasons. From a historical perspective, it would be a fair statement to say that out of all the others doing immersion during that time, John was probably the most popular, and also why the New Testament probably mentions him so much. If John was famous in that contemporary time, to write and say that he was on your religious side would be a good advantage for spreading your message.