Short orders are orders where you're betting on the decrease of an asset's price. If the price of the asset decreases, you earn a profit; if it increases, you lose money.
A short order is created by taking out a loan denominated in the asset that you wish to short, with collateral denominated in a stable currency (like DAI or USDC). The loaned asset is immediately converted to the stable currency. If the asset's price falls, the value of your debt also falls, meaning you need to pay back less money, giving you a profit. If the price rises, your debt increases, and you lose money.
You can also make leveraged short orders, which amplifies the amount of returns (or losses) you make. For instance, if you make a short order with 2x leverage, and the price of the underlying asset fell by 10%, your return would be 20%.
Click "Make Investments" on the manager portal's header, select an asset with the label "Margin Trading", and you will be able to select the short order option, with up to 4x leverage.