Generally machine translations use a method based on linguistic rules, which means that words will be translated in a linguistic way — the most suitable (orally speaking) words of the target language will replace the ones in the source language. However, the users can also make some efforts for reaching acceptable results because first of all the quality of machine translation directly depends on the quality of the delivered source text.
Translation theory suggests that it should be possible to move from the source language's surface level (words, grammatical structures) down to the semantic "deep meaning" and then transfer that deep meaning into the target language using the appropriate words and structures of that target language.
The translation program itself cannot always define which one of grammatically equivalent translation set in the dictionary is most appropriate for each case. It is only you who can help solve the problem!