work the stitch just means you are knitting it or purling it or whatever the instruction says. doesn't really mean anything beyond just doing what the instruction says.
if you go here you will see videos on knitting into the back of the loop. knitting in the front of the loop is just a traditional knit stitch. scroll down and look in the first column for "K tbl" which is knit the back loop. there are several videos right in that section that will help with knitting in the back or doing both in the same stitch.
much easier than it seems when you first see the instruction. i know when i first saw it i though they were crazy!