Learn German: Die Vase steht jetzt auf dem Regal.

The verb stehen describes a state or fixed location (where something is), meaning the vase is currently resting upright. The verb stellen describes the action of placing something somewhere. Since the vase is already on the shelf, we use steht.

Why is it auf dem Regal (dative) and not auf das Regal (accusative)?

The word auf is a two-way preposition. Because the verb steht describes a fixed location rather than movement toward a new destination, we must use the dative case. The neuter noun das Regal changes to dem Regal in the dative.

Could I just say Die Vase ist auf dem Regal?

Yes, and people will understand you perfectly. However, German speakers strongly prefer to describe exactly how an object is positioned. Since a tall object with a flat bottom rests upright, it is much more natural to use stehen (to stand) instead of just sein (to be).

Why does jetzt come right after the verb instead of at the end of the sentence?

In German sentence structure, time words like jetzt usually come as early as possible after the verb. They also come before place information. This follows the Time-Manner-Place rule, so jetzt must go before the location auf dem Regal.