Questions & Answers about Der står en vase midt på bordet.
Here der is a dummy subject (also called an expletive). It does not mean there in the literal location sense. English does something very similar in sentences like There is a vase on the table.
So in Der står en vase midt på bordet, der is used because the sentence is presenting the existence or presence of something: a vase.
A very literal comparison would be:
- Danish: Der står en vase ...
- English: There is a vase ...
Even though der often means there in other contexts, here its job is mainly grammatical.