A variable is a sort of container that holds a value, a string (characters or text), a number or other object references. You can create a value by clicking and dragging on the variable tab at the bottom of the code panel. Then a small window will pop up that allows you to define its type (decimal, integer, text, …), set an initial value and give it a name.

Next time you are assembling a procedure in the code editor, and this procedure also requires parameters (values), matching variables will be suggested in addition to the fixed values you have used so far.