This post shows how an exercise can be solved in the Waltzing Atoms App. Here, I solve on an Android device, iOS follows analogously.
1st step: Start the Waltzing Atoms app, navigate to the exercise of choice and open it:
We are solving a classroom exercise here (not available in the starter kit downloaded with the app). Of course, you can also solve exercises that come together with the app in the same way
I now see the exercise "aspirin" with missing atoms as white slots:
2nd step: To solve the exercise means filling out the missing atoms and complete the molecule. This is done by clicking on the "plus"-icon on the top-left side:
The candidate-atom-slider pops up. In this example only oxygen "O" atoms are available for fill-out. Grab an atom by dragging the chemical symbol in the slider (in this case "O") in the 3D window where the molecule lives:
Now navigate the atom to the empty space and drop it:
When you complete an exercise for the first time, you see a nice animation:
Congratulation for solving your first exercise!