Assets
Assets are kept track of wallet-wide, and can be opted-in to on an account by account basis. Wallets generally show balance, the amount the user has, and value, the worth of said value in the preferred display currency.
Metadata
When a new asset is introduced the wallet can use the RPC to retrieve the name, symbol & decimals. For the native asset on a network this is generally configured network wide.
You can read more about read more about erc20 on the ERC20 page.
Formatting
It is important to get formatting right, refer to the amounts page.
Discovery
A wallet may come across assets that the user has not explicitly defined themselves beforehand. Perhaps because the user just received them, transacted, or interacted in any way. Newly discovered assets should not be auto-added, but rather surfaced in the account asset management flow.