Put the wood slab on a saw horse. Cut off a 1-foot block from either end of the wood slab. Keep this block; it will serve as the leg of the coffee table.
Cut 1-inch-thick wood boards using the circular saw from the rest of the wood slab. Cut 3-foot-long slices. The width of the wood boards will depend on the girth of the wood slab.
Sand the wood boards using the 200-grit sandpaper and the sander. Wear protective goggles to avoid debris flying into your eyes.
Place the 3-foot-long wood boards next to each other on the ground. Nail one slice of wood at both ends of the 3-foot-long wood boards on the ground. This will serve as the table top. Use short nails so that the pointy-end of the nails will not hang out on the other side of the boards.
Place the table top on the 1-foot-tall block of wood you cut off at the beginning. The block needs to stand underneath the table top in the center. Nail the table top onto the block using 5-inch-long nails. Check whether the table top is wobbly. If it is, strengthen with a nail.
Apply the varnish to the wood boards using the brush. Use a face mask when applying the varnish as it may contain chemicals that could harm your lungs. Leave the varnish to dry for one day.