More specific description please

Question

être + descendu [de, sur, etc]
= to get off [something] 
= to get out of  [something/somewhere] 
= to go/come down from/to/into [something/somewhere]

avoir + descendu [quelque chose] ou [quelqu'un]
= to go/come/climb down [something]  
= to take [something] down -> physically moving [something] to a lower position  
= to take [someone / animated being] down -> to shoot them down, to kill them

There seems to be a lot of ambiguity between the English example meanings between être and avoir usage:
 to get off [something] 
= to go/come down from/to/into [something/somewhere]
and:
= to go/come/climb down [something].
Because in English these translations can have very similar meanings, it is unclear to me, hence the ambiguity, a method to differentiate these two.
Could you please elaborate more with a bit more preciseness?
Merci en avance.

Answer

You use "être descendu" in the intransitive form whenever you use a preposition and not a direct object. For example: "je suis descendu de la boîte" -- I got out of the box. But "j'ai descendu la boîte (à la cave)" -- I took the box down (to the basement).

I guess you need to detach yourself from the English and stop translating. Easier said than done, I know, but ultimately there's no way around it.

-- Chris.

Answer

It is difficult to not translate, partially due to the fact that everything on this site is translated. 
Merci.

Answer

Hi Ron - yes, this is unfortunately one of the harder aspects of language when the mapping between two languages isn't straightforward. Chris is right that the only way to deal with this is to try to detach yourself from the English (which is only really there to ensure you understand the meaning quickly).
In general, French is more precise than English, so that may help here. Consider that the same expression is used for trains and cars, whereas we use two completely different expressions for the same thing in English (why do we get out of a car, yet get off a train? The action is almost identical - but the act climbing down, say, a bean stalk is clearly different and we see that reflected in the French).
Prepositions (and prepositional phrases, in English) is one of the areas where there is no logic or rule to help. You just have to learn and become familiar with each in each context.
However, the main take away from this lesson and the related lessons is that if the verb takes a direct object (a.k.a. 'transitive') then we use avoir not être in le passé composé.
Hope that helps!