Google Tasks now has its own app on both Android and iOS. Follow these instructions to learn how to utilize the app. It works much the same as in Gmail.
Download the app. If you are using an Android, go to the Google Play store. If you are using an iOS device, go to the app store.
Once the app is downloaded, sign into your google account to bring up your tasks.
To add a task, click the blue Add a new task button.
Then tap the task to add a due date, description, or subtasks.
It will save automatically once you are finished. If you turn on notifications for the app, you will receive calendar updates as reminders for when tasks are due. You can also click on the menu in the lower left corner of the app to switch between task lists or add new ones. The menu also allows you to mange other google accounts you have logged in on your phone. This is helpful for someone with personal and work emails.