The pattern is doing 2 stitch and 3 stitch cables.
F and B just refers to holding the 1st half of the cable to the front or the back.
On the 3 stitch cables, the pattern really should tell you whether or not 1 or 2 stitches are to be held front/back. If the pattern does not say, then in theory you could do either, just be consistant throughout the pattern. I might lean towards moving 1 and leaving 2.