[Andy]

If you rest the mouse pointer over a button, you will see a small help popup.


Select-through - if on, drag/box selections will select everything under the box. If off only the front stuff will be selected. Try it with selecting some surfaces from a sphere. If on, you'll see surfaces on both sides be selected. If off, you'll only get the nearest surfaces selected. Note that click-select (without a drag) always chooses the nearest item.



Grid snap - used for snapping items to a grid (defined 2nd at the top in File->settings->general). e.g. set the snap-grid to 0.1 and all draw some boxes and you'll see that the sizes and positions are all multiples of 0.1.