Form blue playdough into a sphere. You’ll have to choose a size, remembering that a smaller size will have to be less detailed, while a larger size will take more playdough. You’re starting with blue, because most of the Earth’s surface is covered in water.
For reference, mark the poles and the equator. Two pinpoints at opposite points of the sphere will be the poles, while the equator is a scored line bisecting the sphere between those two points.
Make a greenish-brown color mix and use that to form the temperate continents. You can do this by eye, referring back and forth to the globe, or you can scale more accurately by measuring. For example, if your globe is 24 inches in circumference and your playdough sphere is six inches in circumference, then your scale will be 6/24 = 1/4 of the globe. So if a continent is six inches wide on the globe, it will be 6 x 1/4 = 1 1/2 inches wide on your model.
Form the northern and southern polar regions with white. You may want to add a tinge of brown to Antarctica and Greenland to indicate they are landmasses covered by permafrost, as opposed to the North Pole, which is just floating ice.
Add smaller geographic details. If you want to fill in inland seas and lakes, deserts, and mountain ranges, you can mix colors to represent these features and model them in place.