A ruler is a straight-edged instrument, often made of plastic or wood, which is designed as a guide in drawing straight lines and measuring small increments. There are two majoy types of rulers: the metric ruler and the English ruler. Metric rulers come in millimeters and centimetres, with numbers appearing on the centimeter marks, while English rulers come in inches, with numbers appearing on the inch marks. Here are some instructions on interpreting a metric ruler. 
Instructions
Metric Ruler
1), Count the number of marks between the numbers, remembering that the numbers on a metric ruler represent centimeters. Note that there are 10 millimeter marks between each centimeter mark.
2), Look for the slightly longer millimeter mark in the center of the millimeter marks. This represents the halfway point between the centimeter preceding and the centimeter following.
3), Read the metric ruler by looking for the preceding centimeter, counting the millimeters and using the millimeter as a decimal. For example, a mark four spots after 3 would read 3 centimeters, 4 millimeters---or 3.4 centimeters.

If you want to do some games with your kids at home, then you can try to make a paper holder out of a ruler. This activity is a perfect choice for the materials it uses are the common materials you can find around your house. So it will not bother too much to prepare the materials. Use your creativity to start this activity. 
More Instructions
1), Load a glue stick in your hot glue gun and plug the glue gun into a power outlet. Then Allow the glue to warm up according to the instructions on the package.
2), Lay your ruler on your work space so that it is flat.
3), Squeeze a dollop of glue on the back of two binder clips. Press the clips with the glue on it onto the ruler's right and left edges. Allow the clips to dry.
4), Cut a 12-inch strip of fabric ribbon of your choice with a pair of scissors.
5), Turn the ruler over. Squeeze a dollop of glue on each end of the ruler. Press the one end of the ribbon into the glue on the right edge and the other end of the ribbon into the glue on the left edge. Your paper holder is read for hanging. Clip papers in the binder clips.