"I will climb down from the roof."
Translation:Jag ska klättra ned från taket.
Could you please elaborate on the concept of "object". Did you mean grammatical object? I am sorry. I am confused. Also, in the examples "gå nedför trappan" and "tårarna rinner nedför hans kinder" can one regard the origin as the top of the stairs and the eyes? I would appreciate your help.
Yes, exactly, I mean a grammatical object. It works like this:
[subject] går nedför [object]
So nedför is the direction - "down" or "downwards". The subject is whatever is moving downwards, and the object is that, which is being travelled - like a set of stairs, for instance.
So as you can see, nedför is a direction, and it requires the (grammatical) object being travelled.
In contrast, ned från is also directional, but it requires the origin of the travel rather than the object being travelled.