To name your variable, start the name with a capital letter. Then, follow the rest of the code as you would for any other variable. You may use an underscore character to separate letters, but never start a variable with a number. For example, 123abc is not a valid variable name, because it begins with a number. However, this type of variable name is not uncommon, but it will cause confusion. Case is also very important when naming your variables, as two-layers would not be the same.