Line the table up against the wall where you want to attach it.
Crawl under the table and use a pencil to draw a line where the bottom of the tabletop meets the wall. Draw the line straight across the bottom.
Mark along the line where you want each of the two brackets to go by making a vertical line. For basic, rectangular wood tables, you may want to put a bracket behind each table leg. However, you want the brackets to go in a section where you have a solid piece of wood to support them. Gauge the wood accordingly.
Pull the table away from the wall.
Hold the brackets against the wall so the corner of the "L" bracket is aligned with the penciled in bracket locations. The flat top of the "L" bracket should be flush with the horizontal pencil line. When it is lined up, the "L" bracket will point down the wall and the other side will point straight out into the room.
Make pilot holes using your drill where the bolts will go. Use the holes in the "L" brackets as a gauge. Make the holes for each "L" bracket. Ensure the holes are big enough for the toggle bolt to slide in.
Put together your toggle bolts by unscrewing the spring loaded wings and setting them aside. Feed the toggle bolt through the "L" bracket. Screw the wings back in place.
Fold the spring loaded wings closed and push them into the pilot holes so they pop open on the other side.
Hold the toggle bolt so the wings are snug against the drywall and screw it into place. Line the "L" brackets back up before you tighten the bolts.
Slide the table back into position. It should fit neatly over the "L" brackets.
Crawl under the table and install the screws through the "L" brackets and into the wood. Use wood screws that are not long enough to poke through the top of the table.