Learn German: Die Stelle ist noch frei. - The position is still open.

While die Stelle does mean a physical "place" or "spot", it is also the standard German word for a job "position" or "vacancy". It is often used as a shortened form of die Arbeitsstelle.

Could I use offen instead of frei to say the position is "open"?

You can say Die Stelle ist noch offen, but using frei (which literally means "free") is the most natural and common way to express that a job, a seat, or an apartment is currently available.

How does die Stelle differ from other words for a job, like der Beruf?

Der Beruf refers to your general profession or learned career, such as being a teacher or an engineer. Die Stelle refers specifically to the open role or vacancy at a company that you apply to fill.