the goal is to reduce the expression in the target (the yellow rectangle up top) to zero

grab the tiles down below and drag them through an operator (the four colored sections of the circle in the middle)
then drop them onto the target to perform the operation using the dragged tile on the target
or drop them into a bay (the green rectangles in the upper middle) to store them (there's a limit of 3 terms per bay)

you can keep dragging through tiles and operations to stack up before dropping a tile

drop stuff into the lower right red rectangle to trash it

you can also "flick" tiles!
if they don't already have an operation when you flick them
they will take it from the first operator they hit

doing stuff costs energy; subtraction is the most expensive, while division and multiplication are the cheapest
you can see how much your current operations will cost while dragging a tile
if an operation fails, that also costs a bit of energy
when you clear an expression, you gain some energy

this version might scale better on mobile

this version might scale better on desktop

that's it for now i guess