2. I understand how to BUY and wait for the price to go up.
Buy and wait for price to go up is good but if you are in trading, you must know when is a maximum time you can wait before you must exit your trading position. Because if you wait too long, market will come to a point which has very big change that can be up or down in a blast off or a weak down.
But I don't understand how you make money on SELL.
Buy low, sell higher, it is how you make money with buying and selling, in spot trading.
For example, let's say I believe BTC will go down. So I BUY BTC. And then I wait for it to go down and then SELL.
Don't I lose money?
If you do this with Spot trading, you will lose money because you buy high and sell lower.
If you do this with leverage trading (Margin), you will have profit because you use your bitcoin as collateral for your leverage trading, when you sell, you sell that position with leverage, not directly sell your collateral bitcoin.
However with Leverage trading, risk is much bigger than with spot trading. I don't recommend you to do Leverage trading.