Dearest Berit, I suspect it's a shortened word of the word properties. Like in a play, they have the props -- the chairs, a book, pictures on the walls, a window, a tree. So we, as directors of our plays, bring in the characters and the props. Props is a noun.

There is also props -- a verb -- and it means supports, like this: "He propped up the painting against the wall." Or "he propped his head up with his hand."

You know, it's not so easy to explain what a word means!

Does this help?