how to create a field with two single select drop down options

i see, thank you for your help.
so my understanding is that:
i create field delimiter with name height
then put [cb:userdata field="cb_feet" /] feet and [cb:userdata field="cb_inches" /] inches into description, that would display those two fields in line against height in user profile and will hide code during registration
and in user list i select height, feet and inches for search and style them to appear in line with css
and the same i'll do for registration display

is that right?

which css file i should edit ?

It'll just display the two values next to one another. It does nothing more than that. Please see the below substitution tutorial for further substitution usage information and examples.

www.joomlapolis.com/support/tutorials/107-use-cases/18353-using-substitutions-throughout-cb

To have profile edit, registration, and userlist search fields next to one another the simple solution is using CSS to float one of them or make their rows inline-display and force a width to them. Typically you'll want to add such CSS to your Joomla template CSS file.