The easiest way to add the network is to visit the staking portal, and try to connect your wallet:
The other option is to click the button at the bottom of the navigation menu:
Clicking either of those will bring up a metamask window that looks like this:
Once you click approve, you will see another window that will ask for your confirmation before switching to the network:
Click Switch Network to complete the switch.
To manually add the Polygon network, please use the following set of instructions.
For desktop users: You can see which network you are on by opening the metamask extension and looking at the very top row:
For mobile users: it can be viewed at the top of the "Wallet" tab:
To add a new network on both desktop browser extension and on the mobile app, navigate to Settings and then to Networks. Once you can see the list of networks in your wallet, click Add Network:
Enter the following information into metamask:
Network Name: Polygon Mainnet
RPC Url: https://polygon-rpc.com/
Chain ID: 137
Block Explorer URL: https://polygonscan.com/
Once you click Save, the network will be added, and your wallet will automatically switch to the new network.