The substance he creates is the same as something he is currently touching. For example, he could put a finger on a bar of steel and make a walkway of steel, or he could be touching a plant and make a bunch of grass grow from the floor. He can only do this with solids. Once he creates it, it cannot move by itself, but it will remain where it was constructed, regardless if it's just floating in the air. He could make something he could eat if, for example, he was touching a ham sandwich or something.