Stone is used to create walls, towers, snd other units or buildings. Players can obtain stone by mining it from the ground. It appears as a gray dot on the mini-map. Each stone mine hold 300,000 units of stone, and allows up to 6 workers to collect stone at one time unless you have enabled Advanced Minig (then you can have 7). Stone isn't one of the major recources in Empire Earth, but it is needed in some cases.
A stone mine is the only way in Empire Earth to gather stone. On the mini-map, any white squares you see are stone mines.