First, fasten rails to table. Start with the side rails first and the end rails last. Loosely apply the bolts from the bottom. Do not tighten yet. Align the side rails with the center finishing, then go to the end and tighten the end rails. Then, look down the side rails like looking down a rifle. Tighten slightly and adjust until straight.
Second, apply the spot. The general rule for applying the spot is to measure half the distance of the width and measure that same distance from the end. That is the spot.
The last picture is the recovering kit which has all the items needed for this type of job, Good Luck.