Lending involves supplying assets to the lending pool, which are then borrowed by leveraged yield farmers to perform yield farming. On Extra Finance, lenders can lend various assets (e.g. ETH, USDC) to earn from the lending APY.
The interest rates for deposited assets are determined by the utilization rate of lending pools, following their corresponding interest rate curve. You can find detailed parameters here.
Extra Finance does not charge any fees for deposits or withdrawals, and there is no default lockup period, so you can deposit and withdraw funds at any time. (Please note that if the utilization rate is very high, it may take some time to be able to withdraw the assets until farmers return them.)