Concentrate on your reactants. You aren't being asked for product information, you're being asked what you need to MAKE the product. That's all reactant stuff. The formula on the other side isn't your concern in this problem, except as far as balancing the equation (which is very important here).

If you know the mass of your sulfur, you can figure out the moles. To find the moles, you would do the same procedure as you would do with NaCl, or CH_{4}, or any other atom. Add up the mass of all atoms involved. For fluorine, that would be both atoms of fluorine, and for sulfur, that's all eight atoms of sulfur. It makes sense. If you were finding the mass of table salt, you would add up one sodium and one chlorine, right?

Once you have your moles of sulfur, you use your mole ratio for the reactants. How many F_{2}'s per every unit of S_{8}? There's your mole ratio (and why you figured out the balanced equation). This will allow you to find the number of F_{2}'s you need.

From there, do the reverse equation of what you did earlier to find the grams of fluorine. Remember that you're dealing with two fluorine atoms, not one.

Make sense?