What is the difference b/w this wallet and Coinbase Wallet app.
Coinbase is both an exchange and a standalone wallet.
When you buy coins on the exchange, they go in to your exchange account's "wallet". These coins are still owned and stored by Coinbase in their central wallets, but are credited to your exchange account. Since these coins are in your exchange account, they can be quickly sold or traded on Coinbase. If you want to withdraw them, you have to place a withdrawal request with Coinbase. Since the coins are stored by Coinbase, you do not own the private keys and therefore do not really own the coins, and Coinbase could lock your account or demand more KYC from you at any time.
The Coinbase wallet app, on the other hand, is a standalone wallet app which is separate from the exchange. It generates a seed phrase for back up and allows you to hold your own private keys. Any coins stored in it are under your control because you control the private keys, but if you want to trade or sell these coins then you will need to first send them from your wallet to an exchange (be that the Coinbase exchange or some other exchange).