Well, it depends on the context. Usually "at all" is just added for emphasis. For example, you could say, "there was nothing there at all." The sentence means there was nothing there. Or you could say, "I don't know Spanish at all," which means that you don't know ANY Spanish, not even a little.

"At all" basically means "not even a little." It is often used for emphasis.

You don't provide a context, but it's often used as an intensifier meaning roughly "to any extent", especially in negative/interrogative contexts, e.g. "I don't like it at all", or "Can you hear him at all?"

I think that almost all the situations could be taken care with the translations 'completely', or 'absolutely', or 'in all', or 'really', or 'truly' -- Examples: It is nothing at all (it is truly nothing) No power from the engine, at all (absolutely no power from the engines) This principle must prevail at all the stages of the production. (in all the stages...)

it depends on situations.