Set Grid Planes
These buttons allow you to control where the grid appears relative to the X, Y, and Z axes.
Use this to set the grid to render on the X axis (facing to the left/right).
Use this to set the grid to render on the Y axis (facing up/down).
Use this to set the grid to render on the Z axis (facing forwards/backwards).
Use this to render a grid with all 3 axes.
TIP: You can also enable the Predictive Grid option on the Snap Settings window if you want ProGrids to decide which grid plane to use.