Tap the checkbox to complete a task.

Depending on your checkmark settings, the task may be automatically archived as well.

To explicitly archive a task you can swipe left on the task and tap the More actions button.

Then choose the Archive option from the menu.

If you are viewing archived tasks you can tap the checkmark to re-open the task.

To delete a task, swipe left on the task and tap the Trash button.

If you make a mistake, tap the Undo button.