You can assign names to the dimension variables or you can create your own parameters. You can also create formulas using mathematical expressions. If you do not create an expression at the time you create a dimension, you can use the parameters dialog box to add or edit equations.
Parameters panel
Parameters to open the Parameters dialog box.
Note: Variables names are case sensitive and no spaces are allowed in the name.
Tip: You can use algebraic operators in the equation area or in the Edit Dimension dialog box to create a mathematical formula. Incomplete or invalid equations display in red.
After finishing the sketch, the view automatically rotates to the Home (isometric) view.
Click the Model tab
Create panel
Extrude . Click and drag the gold distance arrow manipulator until the value 20 mm appears in the value input box. Alternatively, you can enter 20 in the field using the keyboard.