This is really a very simple question, and if we work hard, we will easily find this knowledge on the internet. It is confusing that this topic is not closed yet, and many people are still absorbed in explaining and answering this simple question. As far as I can see, no answer is perfect and easy to understand, it cannot be complete and detailed to help a novice understand the bear and bull concept of the market. For basic knowledge, instead of asking others, we should look it up on our own through the internet.