Cable front is a term used to indicate the formation of a left-slanting cable. You will usually see it in a knitting abbreviation like: C4F, which means cable four front.
The number in the instructions tells you how many stitches are involved in the cable. A cable four front, for example, involves four stitches.
To make the cable, you would slip two stitches onto your cable needle, hold the needle in front of your work, knit two stitches, then knit the two stitches off the cable needle.