The prefix nu, when used with verbs of movement, means a direction away from something. It is the opposite of the prefix at, as far as movement is concerned.

nueiti - to go/walk away from smth
nubėgti - to run away from smth
nuvažiuoti - to go (by a transport) away from smth
nuskristi - to fly away from smth
nujoti - to ride away from smth
nuplaukti - to swim away from smth

Moreover, the preposition that it usually goes along with is not iš, but nuo:

Aš nueinu nuo mokyklos. I go away from school.
Dėstytojas nubėga nuo universiteto. The lecturer runs away of the university.
Laivas nuplaukia nuo Lietuvos. The ship swims away from Lithuania.
Laivas nuplaukia į Ameriką. The ship swims away to America.
Arklys nujoja. The horse rides away.
Paukščiai nuskrenda nuo kamino. Birds fly away from the chimney.

Compare:

Aš išeinu iš mokyklos. I go out of the school.
Dėstytojas išbėga iš universiteto. The lecturer runs away out of the university.
Laivas išplaukia iš ežero. The ship swims out of the lake.
Paukščiai išskrenda iš kamino. Birds fly away out of the chimney.