Rube Goldberg machines take a simple process and make it into something very complicated. There can be as many steps as you like, or as few, but every single device will be different from the next (even with the same goal in mind). When it comes to actually building this form of machine, creativity and a knowledge of scientific principles is the key to a successful design and completion.
Gather your materials and begin to set up on the edge of the workspace. Set up the corkboard so the edge hangs over a little. Make it sturdy with heavy books set on the back side. Place the 12-inch-tall box against it. The dowel rod should be taped to the back end of the box.
Cut the string so it measures approximately 36 inches. Cut the yarn so it measures 9 inches at most. Bend the extra-large paperclip into a triangle shape around the empty spool of thread lengthwise. Pierce the bottom of the paper cup and thread the string through from the top. Knot it around the small paperclip on the outside. Place the balance balls on top of the 12-inch-tall box near the table's end.
Build a ramp out of a paper towel tube. Make sure that it is securely held up from beneath on the table. Tape or glue at the top and a book beneath should do.
Place a pushpin into the cork board in line with the bottom of the ramp at the top of the cork board. Pick up the string with the cup. Place this string over the spool. Tape the flag to the end. If the cup is not directly below the bottom of the ramp, adjust it accordingly.
Set the golf ball at the top of the ramp. Adjust the balance balls so they will hit the golf ball and send it down the ramp. Cut a small piece of posterboard and make a rectangle large enough to hold one of the balance balls. Flip up the end and tape it upright at the sides. Pierce the end and put the yarn through it, tied in a knot to hold it straight back. Tie the end to the dowel rod.
Set the candle and holder on the box so they are beneath the yarn. Adjust so that the flame from the candle will reach the yarn to burn it through.
TL;DR (Too Long; Didn't Read)
When designing and building a Rube Goldberg device, work backwards from the goal to the beginning if you get stuck.
Even when properly done, it may take you several tries to get the entire device to work as it should. Plan accordingly.