Here's how it works:
* Get down from: This phrase means to descend from something, like a chair or a tree.
* On fire: This phrase means to be burning or to be very enthusiastic or excited.
* Get down: This word can be used in both contexts. It can mean to descend (like in "get down from the ladder") or to become enthusiastic (like in "get down with the music").
The meaning of "get down" depends on the context of the sentence.