To get started with MetaMask, you'll need to first download the MetaMask browser extension. Once installed, you can use the wallet on the Polygon mainnet or testnet. To add custom tokens, you can use PolygonScan to copy the contract address of the token. Once you have the contract address, you can use MetaMask to import your tokens.
Once you have Metamask installed, the next step is to add the Polygon network data. To do this, click on the "Add Network" option in Metamask's settings. Once added, you'll need to add your MATIC tokens to your wallet.
Then, go back to the MetaMask website and follow the instructions. You'll need to select the Polygon Network in the network menu. Once done, Metamask will notify you that you've connected to the Polygon network. You'll have to approve this message to complete your setup.