Whenever I am tying to make a empty the child of the axis, the whole file get's weird. I would like to extend this animation a bit but I don't know how I manage to add more empties.
Would love to have a fast answer:)!
Edit: Just watch Chapter 3 of this course.
This may not really answer your question, but it may give you the key to continue (even after 10 months :p)
Follow this if you want to recreate the cube+empty:
Load the startup file and select the cube to place it Z+1 Blenderunit. Add 1 Empty (Add lower left corner or Shift+A). Grab (G) the empty and move it X+1 Blenderunit.
Select the Cube and go to Contraints (properties-> the icon left from the modifiers). Select Add Object Contraint -> Relationship -> Child Of. Select your target with the droplet (or whatyamaycallit) and then select your Empty. Tab "Select Inverse" so that the cube goes back to its original location.
The cube in the video shows that it moves only in the X and Z axis and that is rotates along the Y axis. So deselect every XYZ option, except for Location X+Z and Rotation Y.
Now you can rotate the cube with the Empty. Knowing this, you can extend the animation if you wish. If you want to make the cube "roll" into another direction, you need to make sure that the right X/Y/Z blocks are checked and unchecked (rotation and location).