We are doing Aldol condensation, and are asked to find the concentration of the UV-Vis Spectrum. However, I am not sure how to do this. In my lab, it says that methanol and polyethylene cuvette range: 300-700nm are used on the purified product. How would we know what solvent is was, and what concentration to state?

The fact that the range of methanol is stated would make me believe that the solvent is methanol. You can determine the range of concn if you know the molar absorptivity constant. If that is not listed and you have no other information to go by, it is trial and error.