Using Variables:
To add the variable, select the menu item from the Add Variable popup menu in the toolbar that corresponds to the type of variable you want to add.
In the Inspector, find the field you want to bind to the variable. It will have a variable well surrounding it.
Click on the variable well, and in the variable popup that appears, choose your new variable.
Repeat for any other values you want to bind to the variable.
If you want, you can add a variable value in a factory to set that variable to a specific value when building that factory.