When stating that something exists you would use "есть" which means "there exists" or "there is".
Instead, this sentence implies that the listener knows about the bag already so you don't need to state that a bag exists, only where it is. Perhaps you're answering the question "Have you seen the bag?" "Yes, the bag is by the table."
Сумка возле стола uses more often than Сумка находится возле стола. But both sentences sound good. Unlike "Сумка есть возле стола" which nobody says. Besides, for Russian speakers Сумка возле стола and Возле стола сумка have almost the same meaning.
To make a bag known without gesturing a hand in its direction, can either the previous context (which we do not have here) or the demonstrative pronoun. Эта (this), for example.
(addition) While re-reading what I wrote, I saw this is not immediately subtle difference.
1) Сумка (where?) возле стола. 2) Возле стола (what?) сумка.
Accordingly, they are translated: 1) The bag is near the table. 2) There is a bag by the table.
I have never heard a native English speaker say either "The bag is near the table" or "A bag is near the table." "The bag is by the table." "There is a bag by the table." I suppose it is meant to clarify the concept in Russian, but those sound odd to me.
Сумка рядом со столом ‧ A bag is next to the table. ‧ There is a bag next to the table.
I'm not a native speaker but I think it's because the word сумка comes first. Thus, it is a "known" bag; it is not new information. So, it is "The bag is near the table." If it were written "Возле стола сумка" it would translate to "There is a bag near the table."