How do you reference an element in Revit?

I feel the question is not that clear. Can explain further what exactly you need?

thanks

• Elements in the main model and in the primary option can reference each other.
• Elements in a secondary option can reference elements in the main model.
• Elements in the main model cannot reference elements in a secondary option. Therefore, elements in the main model do not change their shape or properties when you are editing a secondary option. For example, if you sketch4 walls in the main model and then sketch a roof in a secondary option, the walls do not regenerate and attach to the roof.
• If main model elements need to update with and reference elements in secondary options, move the main model elements into each design option (or selected options) in the design option set. Then edit each design option to modify those elements as desired for each design. 
• View-specific elements can reference elements in design options. For example, you can dimension elements in a view that is dedicated to a design option.