From your main calendar view, tap the menu bars at the bottom right.  Choose Settings>calendar views.

Now scroll down to the 'sorts tasks in calendar' option and choose how you want the tasks to be viewed.  
Then scroll past that to the 'show tasks in' options and choose the areas you want your tasks to show. 
Scroll past that and choose the 'task display logic' for those tasks.

The next few options are for specific tasks such as starred, overdue, and undated.

If you want to see completed tasks quickly in your calendar view, tap the menu bars at the top right of your main calendar view and choose the 'show completed' option.  Choose the menu bars again and choose the 'hide completed' option to make those hidden again.