Open Power point and create a new presentation. Make a blank slide and set the transition to advance after 1 second. Click Apply to all.
Draw the first frame of your animation. This one is important - it is the frame that all of the other frames in this scene will be based on. Take your time with it.
Duplicate the slide, and make a very slight change in this slide for the progress of the animation. If you had a ball falling, make it go down one or two places.
Do not duplicate the new slide and keep going. For things like gravity, make the motion stronger each time, eg: changing it more and more. The most catastrophic thing is to make things go too fast, so don't be afraid to take a lot of slides to do one thing - you can always delete them later.
Add in sounds and other details, then make a beginning and ending slide, maybe even an opening sequence.