Question

Is left is conjunction or preposition

Answer 1

"LEFT" is a preposition.        It can be used as a noun or adverb or adjective.
It is an Adverb,   if the word "left" is associated with a verb. 
It is an Adjective,   if it is associated with a noun.

examples

Adverb :       Turn left  here.    Left turn.
Adjective :       Left hand.     To my left side.

Answer 2

Answer:

Left is a preposition because it do not join sentences so it can't be a conjunction .It tell a location so it is a preposition