MetaMask is a non-custodial cross-chain wallet that enables your Trezor device to manage and sign transactions on Ethereum and Ethereum virtual machine blockchains (EVM) including Binance Smart Chain, Polygon, FTM, and AVAX.
When your Trezor device is connected with MetaMask you can use it to manage your smart contracts and DApps, unlocking the power of MetaMask with the security of Trezor.
Since Trezor secures your private keys, you no longer need to rely on MetaMask to keep your keys safe. Your keys remain only in your Trezor device, protected by the hardware.
The following video shows you the basics of using various types of accounts in Metamask:
You can also use MetaMask to sign messages. Message signing allows you to sign in into certain DApps, such as CryptoKitties - see the short video below.
The Trezor accounts (the yellow and the blue one in the picture) are the same accounts are generated in Trezor Suite. These are Trezor generated accounts and can be recovered only by using a Trezor recovery seed.
All three wallets mentioned (1, 2, 3) would differ from your currently used Trezor Wallet. Only the first MetaMask account (1) can be used without your Trezor because it is independent of Trezor completely.
However, as for other accounts (2, 3) you may see, the related Trezor device must be connected (either with the appropriate seed and/or with the appropriate passphrase). Otherwise, you will not be able to sign any transactions within these accounts due to missing the appropriate private key stored on Trezor.
If you are unable to access that account by using Trezor Suite, then the account you want to access via MetaMask is not part of your Trezor wallet.
The following video also shows how Trezor will always generate the same wallet, accounts, and addresses when the same recovery seed (and passphrase) is used: