When making a standard crochet stich you insert your hook into the stitch and through both loops of the stitch as shown below...
|standard crochet stitch|
When you are instructed to use the front loop you insert your hook through the front loop of the stitch only.
|Front loop (insert hook only through the front loop of the stitch in the previous row)|
|back loop (insert your hook through only the back loop of the stitch in the previous row)|
|decorative ridge created by working all stitches in the front or back loop only|
|deep ribbing created by alternating rows in the front and back loops|
Any questions? Use the comments section and I will respond as quickly as possible!