Depending on your part geometry, you might be able to make better use of a given stock size by nesting your parts. Nesting involves flipping the part around so that it can nest in the blank spots between other parts and can minimize waste in cutting some parts.
Setting Nested in the Layout dialog box changes the picture and adds some more parameter fields.
X /Y shift is set for the inverted row. The important concept is that you don’t set space directly between neighboring shapes. That parameter was handled earlier when you specified how many repeated columns and rows to use. For shift spacing, you are setting the distance between the two rows’ top edges (Y shift) and the columns’ right edge offset (X shift). You probably will need to adjust your X and Y spacing in addition to the X and Y shifts to find the optimum spacing. Don’t overlook negative values either.