Watch the video Jan mentioned. That will be a big help. You will want to use a smaller needle than you knit the main body on. It sounds like they give you at least 2 sizes of needle in the pattern. If you used a different needle to get gauge with than given use the same distance between the sizes given. For instance if it says to knit the ribbing on a 3 and the body on a 5 and you have to use a 4 to get gauge, go down two sizes to a 2 for the ribbing and the bands.
I’m am not mathematically inclined but there is a difference in the size of the sides of the stitches, like along the vertical edge of a sweater, and stitches that you would pick up to knit perpendicular to that front edge, like the band. Your pattern says pick up 2 stitches for the band from every 3 rows of the front, so you are to pick up in first row, then in the next one as well, then skip one. Count 1,2, skip all along. I usually find 1,2,3, skip works well, but different sizes of yarn need different ratios, so try it the way they say. I like a pattern that doesn’t tell you to pick up some exact number, the way yours is written is easier.
The video may address where you insert your needle to pick up the stitches, but let your eyes help you. What you see is what you get. You usually want to have a line of picked up stitches that follows right along a vertical stitch and doesn’t jog around to get a good look. It is easy to take out a stitch and redo it, or even the whole row if you need to and try again.
Picking up stitches is like knitting up a loop from an invisible needle, stick your working needle into the fabric, yarn around and pull up a stitch loop onto the working needle. Keep doing that all along the edge to get stitches to make the bands from. It’s fun.