Okay, you started out with 11 stitches and knit however far it says. Now you are at the window placement. K3, bind off 5 and knit the rest. You will have 3 on each side with an open space in the middle. The far side (the first 3 stitches you knit) of the gap, put those 3 on a holder. Work only on the one side of the gap with the yarn attached for 1", have the last row you do be a purl row. You will end up at the inside edge of the the gap. Cut the yarn. Put the 3 stitches that you have just been working for the inch on a holder. Put the other 3 stitches that have been waiting on a holder onto the working needles. Starting at the edge closest to the gap with the purl side up, bring up a new end of yarn and start working with it (things may seem loose right there for several rows, but leave a tail when you begin with the new yarn and you will be able to snug it up and make it look good when you are finishing up) by purling the 3 stitches. Work back an forth in stockinette stitch for an inch on these 3 stitches. The last row you do should be a knit row across the 3 stitches, cast on 5: Put the needle with the 3 stitches on it in your left hand,* insert the empty right hand needle between the first 2 stitches at the end of the left needle tip, right under the needle, not into the stitches but under the needle between the stitches. Yarn around like you were going to knit it from that position and when you pull up a new loop put the loop on the left hand needle and repeat from the * until you have cast on 5 new stitch loops. Now put the 3 stitches that have been waiting on the holder onto a needle and knit across them so that you now have the original 11 stitches back and everything back into one piece. Work another inch over the 11 stitches, ending with a purl row as the last row.
This site has a free video that shows how to do the cable cast-on (which is the one I gave you) under the video tab listed under "cast-ons".