To sign use, begin by closing your non-dominant hand into a fist in front of you, then tapping your dominant hand forming the ASL letter U sign, palm side facing you, on top of your non-dominant fist a couple of times at the wrist area. It is as if you are saying that whatever tool, object, or device you are using is hard at work fulfilling its duty or purpose.
Use is signed a bit like work, so be careful not to get these signs confused.
Teach your advanced toddler the use sign when you want to emphasize that they can or should use the object in question for a particular purpose. "We use soap to wash our hands or take a shower." "You use your spoon and bowl for soup." "We use a pencil and ruler to draw straight line, squares, rectangles, and triangles."
This is a useful flash card taught best in context, in conjunction with the actual object, tool, machine, or device that is being used for a specific purpose.