Asides a few minor details like navigation, the mobile app works exactly like the web app. You can buy, sell, send, receive and store different cryptocurrencies on the Quidax mobile app.
Currently, the Mobile App has the instant buy/sell feature, which you can use for real-time and immediate cryptocurrency buy/sell transactions. While the Web App has both the Instant Buy/Sell feature and the Order Book Exchange.
The Order Book exchange would be made available in an updated version of the Mobile App.