The block of wood is supposed to be shaped ito something resembling a streamlined, Indy-type car. I don't know how this block of wood looks these days, but 45 years ago (!) it was an extruded square with a cutout where the "driver" would go (think 60's vintage Bugati).
What we did was get a coping saw, and cut the block down to a desireavle shape, then either whittle or (better) wood rasp down the corners to something rounded, sand off the rough edges, paint, and atach the wheels. Voila! A Pinewood Derby racer.
Now for the details. There is a maximum weight that the racre can have. Get the weight as close to the max as possible. (My dad and I stuck a plug of lead into the cockpit until the weight was as close to the max as possible.) The wheels are nailed into a slot on struts tht come out of the main block of wood. Don't drive those nails too deeply into the struts or they will bind. spend some time spinning the wheels to "polish" the places on the nail where the bearing surfaces are.
Also, when I did it, we were not allowed to use power tools. Hence, the coping saw, wood rasp, etc. If you are now allowed to use power tools, perhaps a band saw would be easier than a coping saw (with the appropriate increase in cost...).
HTH. Have fun...