A tape diagram is a visual way to solve word problems in mathematics, and the way to make one is to draw colored blocks to represent the quantities in the word problem. Redrawing the colored blocks an appropriate number of times makes it easier to solve the word problem.
The best way to understand tape diagrams is to use them to solve an example problem. Ratios are a common topic in basic mathematics word problems. For example, suppose a word problem states that Jill wants to make some lemonade, and that for every cup of sugar, she needs to use three lemons. That is a ratio of 1 cup of sugar to three lemons. The problem then asks how many cups of sugar Jill needs if she has 12 lemons. You could use a tape diagram to solve this problem. First, draw a small white square to represent a cup of sugar and a green rectangle three times as long to represent three lemons. This is a visual illustration of the ratio. Then, copy the green rectangle four times to represent the 12 lemons that Jill has. Finally, copy the white square four times to represent the sugar that she needs. You can see from the diagram that Jill needs 4 cups of sugar if she has 12 lemons.