Orientation is a relatively new word that was derived in the 19th century from orient, which means to point yourself in a specific direction. Hiking with a map and a compass is sometimes called orienteering, referring to hikers' use of those tools to orient themselves.

Where did the word oriented originate?

The noun “orientation,” in turn, was derived from the 18th-century verb “orient.” The foundation for all these words is the noun “orient,” first recorded in the works of Chaucer in the late 14th century. It originally meant a region situated to the east.

Why do the British say orientated?

People say orientated because they hear the word orientation and think that's the verb made from it. It's called a "back-formation".