The caliber will be stamped around the midsection of the die where it isn't knurled.
DO NOT USE A METAL HAMMER! The die will damaged! Use a leather, plastic or wooden mallet to drive the case in and out.
Follow the instructions exactly and wear safety glasses. Primers can pop.
Identify each of the parts, particularly the rods. The rods are different diameters and can jam in the case if they are mixed up.
After you have resized the first case, take it, and test to see if it will chamber in your gun. If you have a revolver, test all of the chambers. Some brass, fired in a large chamber may not be resized enough by the Lee die (or other dies).
Don't buy a lot of components at first, 100 lead bullets, 100 primers, a can of powder, and some fired brass to start with until you get a feel for reloading.
I suggest your first powder be 'Trail Boss'. It is very forgiving of mistakes. It is nearly impossible to overcharge a pistol case with it.
Be careful, some years ago Lee changed the size/calibration of their dippers. They changed from cubic inches to cubic centimeters. Make sure your dipper matches your loading chart. You would be better served in buying a set of new Lee dippers that are sized for modern powders.
Have fun, be safe!
M.