Once in the polygon tab, be sure the Mumbai Polygon testnet is selected in your wallet. You will need some Matic testnet tokens and some Fake Dai tokens to test the builder and manage a demo pool. Click Get Matic Testnet to go to the faucet to get Matic testnet tokens and then click Get Fake Dai to receive some Fake Dai tokens. Then choose the yield source and the underlying token you want your pool to work with and click the Create Button. For demo purposes, there is only one yield source and underlying token available.