If you're connecting to the Matic network for the first time you'll need step 1. If you only need to switch networks, jump to step 2.
If this is your first time using the Matic network, you will be asked by Metamask to add the network. This allows the network to be used within Metmask. Go ahead and approve. Once added, if it doesn't automatically connect, you may need to refresh the page and click the Connect Wallet button at the top right of the Augur Turbo UI. Now you're ready to trade!
If you come to Augur Turbo and your wallet isn't already set to the Matic network, you'll be prompted by Metamask to switch to the Matic network. Click the Switch network button. Now you're connected to the Matic network, click the Connect Wallet button at the top right of the Augur Turbo UI. Now you're ready to trade!