If you are looking to bridge assets from the Ethereum Network over to Polygon (MATIC), please see the following link:
Once connected with your wallet, please click on "Polygon Bridge."
You will need to switch to Ethereum Network in order to bridge over tokens from Ethereum to Polygon Network.
Just follow the instructions when bridging over Ethereum tokens to Polygon. (Vice versa).
Important: You will need $MATIC in your MetaMask wallet in order to conduct any transactions on Polygon.