You can access Kintone from Safari for iOS or the mobile app. You can use your iPhone or iPad to check notifications or post on Kintone anytime, even when you are on the go and there is no PC available.

If your Kintone is customized with API and JavaScript or if you want to use multiple tabs, Safari for iOS is suitable for your needs.
On the other hand, the mobile app allows you to receive push notifications.
Use whichever suits your usage better. You can also use both of them.

For details on how to use Kintone on Safari for iOS, refer to Using Kintone on Safari for iOS.
For details on how to use the mobile app, refer to Using Kintone Mobile App for iOS.