the screws are meant to keep the slick from spinning on the wheel but isnt 100% needed. Tubes arent absolutely needed either. many guys just run the slick, many just run the slick with screws, some run tubes and slicks, you get the idea. its a matter of preference really and power level.
if you go with the tubes, make sure you rub them down with baby powder before putting them on (They tend to bind up and then tear if not) and rub the slicks down with DAWN before mounting them.