Well, the way I see it is that, just like our native languages, there are 'idioms' and different ways of saying things, slang and what-have-you. I too have found that the online translation tools can be confusing - one thing I find sometimes helps, is taking what it has given you as the translation, and putting that back in to translate it back the other way... so if you type in something in (say) Spanish and get an English translation, try sticking that English translation back in and getting the Spanish output... sometimes that gives you a better idea of what it is trying to say. Does that help?
I personally don't worry too much (certainly at the stage I'm at with Swedish) with figuring out all these different combinations - I am aware of them, I'm aware that there are different ways of saying the same thing, and the more I delve into the language and learn from different tools and books etc, the more the differences and 'idioms' become clear. That's why I like to learn from a variety of sources because I feel I get a more 'rounded' knowledge of the language that way.
Hope that helps