In Metamask go to Settings > Network and add the following information.
Network Details
Add to MetaMask through Chainlist
Network Name: Gnosis
RPC URL: https://rpc.xdaichain.com/
Chain ID: 0x64 or 100
Currency Symbol: xDAI
Block Explorer URL: https://blockscout.com/xdai/mainnet
Explorers
Bridge
Swaps
For gas fees you need xDAI, you can get some for free in the faucet.
