http://astroventure.arc.nasa.gov/DAP/index.html Start at the Tutorial – once comfortable, move to Design a Planet REGULAR.
Before clicking on any of the star choices, make sure you click on each star inside the circle to learn about each – then make a choice.
Before choosing a distance, make sure you click on the items inside the circle to learn more before choosing.
Before choosing a mass, make sure you click on the items inside the circle to learn more before choosing.
Before choosing if there are volcanoes present, make sure you click on the items inside the circle to learn more before choosing.
Before choosing if there is active plate movement, make sure you click on the items inside the circle to learn more before choosing.
Before choosing if there is a supply of water, make sure you click on the items inside the circle to learn more before choosing.
Before choosing if there are producers present, make sure you click on the items inside the circle to learn more before choosing.