A bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle.

Fork is the two-pronged thingy that holds the front wheel.

Depends on if the fork is threaded or threadless. Regardless of which www.bicycletutor.com will show you how.

... since the first bicycle, the "Walking Maschine" in 1817.

[See images at the link below]

In bicycle-speak, dropouts are the (usually) slotted ends of a fork and rear triangle of a bicycle that holds the wheels.