Open MetaMask and click the list of networks at the top, then select "Add Network".
Fill the Endpoint Information
You will be prompted for additional information. Use the table below to complete the step. Below you will see multiple options for RPC URL and Chain ID corresponding to mainnet vs testnet, and the various shards within each.
Use the RPC URL and Chain ID of Shard 0 if you want to send/receive transactions from exchanges or do any staking transaction type.