A row counter is a little gadget that help you keep track of how many rows you have knit. I have a couple of this kind
that slide onto the needles. Once you complete a row you turn the little dial. They are several types, but they all do the same thing... help you keep count! Not "necessary", but very handy to have.
Or, they may be referring to this
type of tool to help you figure out how many stitches you have per inch, which is very important when trying to measure gauge.
No, you do not need a cable needle to make cables. Any small object that can hold the stitches for you will work (cable needle, stitch holder, double pointed needle). It's whatever works best for you. You can even make cables without using a cable needle/stitch holder! (Check out the video about halfway down on this page