The 68 is the frame's bottom bracket shell width in mm and is the standard width for all English threaded road frames and most English threaded MTB frames.

The 118 is the spindle length in mm and determines where the crank arms are located. A 126 mm spindle used with a crank that requires a 118 mm spindle will place the crank arms further from the frame and will alter the chain line on the drive side. You should use the correct spindle length or very close to it.