Measure the space where your table will go using the measuring tape. Give yourself enough room for chairs. Allot about 1 foot all around for chair space. The measurement you took will serve as the diameter for the round table.
Mark a center point on your wood, and halve your diameter measurement. From the center point, measure the length of the radius and mark your points. Do this a few times, and connect the spots to create a full circle. Cut out the circle using a table saw or regular saw. This is now your table top.
Sandpaper your table top until it is smooth.
Cut your 2-by-4 into four 36-inch pieces. Sand them and stain them. These will serve as your table legs.
Flip your table top over, and divide it into quarter pieces lightly using pencil marks. Make a point at the end of each mark, about 1 inch away from the table's edge. This is where each of your table legs will sit.
Place your table leg on the underside of your table top, and line up your L-shape bar. Screw in two of the L-shaped metal bars on either side of your table leg. Do this for all four legs. You can also skip the L-shaped metal bars, and instead just screw the table legs to the table at an angle.
Stain your table, and let it dry.