well it depends on case and also preposition and place это на столе= it is on table

это под столом it is under the table это за столом it is behind the table они говорят о столе they are talking about the table

столе is more prepositional and столом is instrumental под means under and anything after is always instrumental за is behind and like под is instrumental about 70% time с is with and you use intrumental when you wanna say with something or by how you did something ex я работаю переводчиком i work as a translater я с друзями i am with friends

на means on or at and it has different cases depending from time to time please let me knowif you need more explaining i can do a lot better

Depends on the preposition

на столе

в столе

о столе

but

под столом

над столом

за столом

со столом (with the table)

still

из-за стола

из-под стола

со стола (from (the surface of) the table)

yet

к столу

по столу

etc. etc.

stolom would fit when saying "The cat is under the table" or in Russian: "кот под столом"

stoleh would be used when saying "the cat is on the table" "кот на столе"

I don't know why though.

on the table (на СТОЛЕ)

sit by the table (сижу за СТОЛОМ)