If you know what you're doing, you can start entering your subcircuit starting with the .SUBCKT statement and ending the .ENDS statement. This subcircuit will need to be in Berkeley Spice 3f5 format with XSpice extensions. Otherwise, copy and paste a subcircuit into the window. You can get the subcircuit text for an existing simulation model by editing the simulation model and copying its text.
Now all you have to do is incorporate your own parameters into the subcircuit. Enter your [[parameters]] in the form of a parameter or formula. All custom parameters must go in between the curly brackets {}. For example, if you had two parameters called X and Y and wish to have them added together in a subcircuit, the formula would be {X + Y}. Or getting fancier, you add X and Y and then multiply by 2. The formula would look like this: {(X + Y) * 2}. All standard mathematical operations are supported (+,-,/,*), power of (^), and any other operation supported in the graphing plot expression module of the Workshop. In the example below, note that the {voltage} has replaced the regular voltage number.
Once you're satisfied that everything is correct, click OK and continue to the next step.