Every morning you will see a popup message that asks you to take a minute to plan your day.  If you click on it, it will open Today view, which is a simple, clean To Do list that you can use as a fresh start to every day.  It looks like this:

The best way to use this feature is to just jot down your tasks for the day off the top of your head.  As you complete tasks throughout the day you will mark them complete.  Anything you don't get to will automatically roll over to the previous day.

If you click on the Yesterday / Earlier link at the top you will see all of your previous tasks that haven't been completed with an option to 'move to today'.

You can open Today View any time by clicking on the Today button at the bottom of your screen, or by using the keyboard shortcut CTRL-Space.

How do I disable the daily popup message?

To disable the daily popup, open Sortd in full screen mode, then go to settings (icon at the bottom left).  Under the General tab you will see an option for 'Daily popup to plan your day' - set that to off.