You have to select Ethereum Mainnet in Metamask as your network
You might need to refresh the page after doing so
Choose a token from the list that you would like to bring over
You can bridge any token that is not on the list too. Simply add it by address first.
Approve/unlock: you need to authorize the bridge contract to manage the funds. This you have to do for every smart contract in general so it's a common practice.
Tip: Enable infinite unlock in the settings so you have to do this step once and never again for the same address. Otherwise you will need to do this each time you use the bridge and pay like 30 bucks on the Ethereum mainnet. Not economical
Transfer! After your transaction is mined on the Ethereum mainnet, wait for the confirmation time to pass and the bridge validators to pick it up.