Summarize the following:
To start making a rectangular shaped mold, first gather your materials. You should be able to find the materials for this mold at most craft stores. For this mold, you'll need the following:  Two pieces of 1⁄2 inch (1.3 cm) thick craft wood, cut into 12" by 4" length  Two pieces of 1⁄2 inch (1.3 cm) thick craft wood, cut into 3 1/2″ x 4″ length  One piece of 1⁄2 inch (1.3 cm) thick craft wood, cut into 3 1/2″ x 11″ length  Wood clamps  Wood glue You may not find craft wood cut into the exact dimensions you need. You should be able to ask someone at the store to trim the wood down for you. If this option is not available, you can cut most craft wood on your own with a small handsaw.  Measure the wood using a ruler or measuring tape. Draw a line marking the dimensions with a pen or pencil. Use your handsaw to gently saw along that line. If the sides are rough, use sandpaper to smooth them down. Sand paper is rated by grit number. The higher the grit number, the stronger the sandpaper. As craft glue is fairly soft, you do not need a high grit sandpaper for your soap mold. Stick to grit levels below 100, as anything above a 100-level grit is best used on large furniture. Once your wood is cut into the proper dimensions, you can begin assembling your mold. To start, assemble the sides of the wood to form a rectangle.  The 12" by 4" boards make up the longer sides of the rectangle. The 3 1/2" by 4" sides make up the shorter sides. The shorter sides will fit inside the longer sides.  Take the 12" by 4" boards. Place a line of wood glue along each 4" side. Then, place the 3 1/2" by 4" sides between the 12" by 4" boards, creating a rectangle-shape with your boards. Use the wood clamps to secure while the wood is drying. Once the glue is dry to the touch, and the rectangle feels secure without the wood clamps, you can add the bottom board. The  3 1/2″ x 11″ board fits inside the rectangle. Run some wood glue along each side of the bottom board and then place it inside the rectangle. Use wood clamps to secure the board in place. If your board feels flimsy, use a cordless screwdriver to place four screws into the board where the sides connect. This will further secure the board, as wood glue may loose strength over time. Once you've assembled your board, set is aside and let it dry. To be 100% sure everything is dry, it's best to set your board aside overnight before use. Once you're done creating your board, you can use it to make soap. Make sure to line your board first, as liquid soap will stick to wood. You can use parchment paper or trash bags to line your board. It can take soap anywhere from a few hours to a few days to set. It depends on the soap recipe you're using. Once the soap is set, simply remove it from the board. Set it aside for 3 to 4 weeks to allow it to dry completely. In the event your box leaks, examine the area where the leak is occurring. You can seal this area up with masking tape, duct table, or extra wood glue. Also, you can deal with leaks by lining the box with parchment paper before use.

Summary:
Gather your materials. Trim the wood down, if necessary. Create a rectangle out of the sides. Glue the bottom piece in place. Let dry. Use your mold to make soap. Address leaks.