This tutorial will show you how to access the "My Collection" shortcut from within the Standards Builder.
Once you've logged in, go to the navigation menu on the left-hand side of the screen and select "Standards Builder."
From here, once you've added your stems and given your assignment a title, you will see the green bar that says "Saved to My Collection."
If you click on this green bar, it'll take you to your "My Collection" page with the assignment already saved that you're currently working on in the Standards Builder.