A naive person; a greenhorn.
"The new hire's naive approach to managing clients quickly earned him a reputation as a complete greenhorn in sales."
inexperienced
"Many volunteers felt naive about the complexities of running a charity before their first summer shift."
lacking information or instruction
"lamentably unenlightened as to the laws"
not initiated; deficient in relevant experience
"it seemed a bizarre ceremony to uninitiated western eyes"
"he took part in the experiment as a naive subject"
Lacking worldly experience, wisdom, or judgement; unsophisticated.
"The naive traveler walked straight into a tourist trap without realizing he had been cheated out of his money."