From here click on any of the available markets and deposit your tokens into the reserve.
Each asset has market specific parameters detailing the Maximum LTV, Liquidation Threshold, Liquidation penalty, and if the asset can be enabled as collateral or not. Submit the review transaction button with the specific amount of tokens to deposit.
Important: SPECIFICALLY FOR METAMASK you must set both the Max Priority Fee to 250 GWEI and the Max Fee to 250 GWEI or else your transactions will fail for both "approve" and "deposit." Ignore the warning messages. This is not an issue for other wallets. Detailed below: