how to highlight a single box

click the first cell of the set you want to highlight, then hold the command key (the key adjacent to the space bar)) then click the other cells you want to add to the selection.

if you want most cells selected and only a few NOT selected, then select one cell to activate the table, then type select the menu item "Edit > Select All", then hold the command key and click the cells you do NOT want in the selection. the key combination <command> + click changes the selectness of an item (whether it is a cell, a table, a shape, a file.