The term First Officer refers to a commercial airline pilot who flies as the co pilot (second in command) alongside the Captain. A pilot usually begins as a trainee or cadet then earns a Commercial Pilot License (CPL) completes required flight hours and ratings. Once those are done and depending on airline demand they can step into their first role as a First Officer.
The path to starting as a First Officer typically includes:
Finishing 10+2 (preferably with Physics & Maths) if in India.
Getting a CPL along with necessary instrument and multi engine ratings.
Accumulating sufficient flight hours (often through training instructor jobs or small plane flights) and clearing medical and other regulatory requirements.
Then applying to airlines once selected and type rated for a particular aircraft you join as a First Officer.
The length of time varies widely depending on training hours logged and airline hiring needs.
After finishing CPL and initial flying hours some pilots may get a First Officer posting within 12-18 months (if hiring and training permit).
For many gaining enough experience and required flight hours may take 1-2 years (or more) from the start of training before getting the First Officer job.
Starting as a First Officer gives a new pilot essential real world experience: handling flights working under a Captain's supervision learning cockpit protocols communication safety procedures all while building flight hours. This role acts as the launch pad for a long aviation career with good performance and hours a First Officer can eventually become a Senior First Officer and later a Captain.