When the mouse hovers over a tile in the grid, changes that tile's color from white to red.
This demonstrates one way to use the Process List node. First, the center point of each tile is calculated using Make Parametric Grid. Every time a frame is rendered, that list of tile points is checked to see whether the mouse is within range, which determines the color. Then a layer is created for each tile, and it gets added to the output list, which then gets rendered to a window.