Expanding a little on iCake's answer, I would summarize the sitting verbs this way:


  • сидеть = "to be (unmoving) in a sitting position" [intransitive, and expressing где?, "where"]
  • садиться / сесть = "to sit oneself down" [intransitive, but expressing movement: куда?, "to where"]
  • сажать / посадить = "to put into a seated position; to help someone sit down; to plant; to imprison" [transitive, and also expressing куда?]

And finally:

  • садить = Rather old-fashioned-sounding equivalent of сажать



So, садить is not wrong, but nowadays it's probably better to use сажать in most situations. For instance, I think it's correct to say Стюардесса сажает пассажиров, "The stewardess is directing passengers to their seats."

P.S. сидеть, "to be sitting," does have various perfectives that add different shades of meaning, but it doesn't really have a "neutral" perfective like садиться /сесть and сажать/посадитьdo.