There is not much of a picture in the roster cited above, showing a few weeks' active duty service.
All able-bodied free white males aged roughly 16-60 (varies by time and place) were required to be available for militia duty for defense within the County. Active duty for militiamen was not common. Most militia rosters just document those who showed up for regular drill and nose-counting (not active duty service).
The more difficult task is to prove that the person on the list is the same individual as a person by that name whom you may have proved to be your ancestor. As a great many have found, "same name" very often is not "same person."