Airsoft was invented in Japan in the early 1970s (making it older than Nerf Blasters and Paintball.) by a Japanese photographer, who was an avid shooting enthusiast. Airsoft spread to the UK in the 1980s and then to America shortly after.
For a more indepth read and more indepth info check out the wikipedia article!
The basic gear for Airsoft is simple.
-an "imitation" gun
Just like with Paintball and Nerf, there are plenty of ways to play it but the 3 most common are:
=Team Deathmatch: its team against team. typically there are 2 teams that fight each other.
=Capture The Flag: often shortened to CTF, the objective is to get the enemies flag from their base to your base a certain amount of times.
=LARP: LARP, Live Action RolePlaying, is a game mode where players Role Play, act out, a character at a place. examples are: Wild West, Apocalypse, and more.
There is tons more ways to play such as MilSim but the three shown here are the more common ways of play and theres always the "at home" or "with friends" ways of playing.
Players in the 'safe zone' between games
Airsoft players firing at an objective