Buying up is easy to understand, that is, I have a hunch that a commodity will go up, so I buy a batch of this commodity now, and then sell it when the price goes up to earn the middle price difference. Similarly, in practice:

Buying up is the expectation of buying up. If it really goes up in the future and there is positive value-added, it will be earned. This is a standing order, specifically a buying and opening order.

Buying down is the expectation of buying down. If it really falls in the future, it is a negative appreciation and won. This is short selling, which specializes in selling open positions.

If you think the futures price will go up, go long (buy and open positions), go up (sell) and close positions, and earn: price difference = close positions-open positions.