In the United States Air Force airman first class is an enlisted rank above airman and below senior airman with a pay grade of E3. The insignia for this rank is two white downward-facing chevrons (so that it looks like a V) centered on a blue circle with a white star inside. An airman first class is addressed as "airman" and it is abbreviated A1C.
An airman first class is in the process of acquiring the skills necessary to succeed in their career field and must conform to Air Force regulations. They are supposed to be role models for their subordinates.
Compared according to the NATO rank structure, an airman first class has a rank code of OR3 and has no equivalent in the Royal Air Force.
Airman ← United States Military Ranks → Senior Airman
General Henry Harley ("Hap") Arnold Award
General Henry Arnold was a champion of air power leading up to World War II and one of the leaders of the push that created a separate Air Force.
Continuing on the road to competence, an airman first class continues to learn more drill and start to look kind of like they know what they're doing. They can be assistant element leader if they're ready.
An airman first class wears the same insignia as the airman except with two chevrons instead of one. The Arnold ribbon has thin red stripes on the outside, two thin white stripes closer in, and is solid blue in the center.
They are addressed as (surprise!) "airman" and abbreviated their grade C/A1C.
Advancement to senior airman is much the same as advancing to airman first class -- 70% or higher on the leadership test, satisfactory cadet physical fitness test (CPFT), moral leadership class, and an aerospace module.
Cadet Airman ← Civil Air Patrol Cadet Grades → Cadet Senior Airman
SOURCES:
Wikipedia: Airman First Class, Comparative military ranks
Grunt's Military: Air Force Enlisted Rank Insignia
CAPP 151
Leadership: 2000 and Beyond
CAPP 52-18
CAPR 52-16
Personal knowledge