Question: How do I get Sentences to translate?
It is a rather irritating feature of the user interface that, as far as I can tell, you can't see where translation work is available without going into each subject area to check. After all, Duolingo wants us to do translations, doesn't it?
UPDATE ON 20/04/12 - There is now a 'Translations' tab between 'Home' and 'Questions'.
If you are asking for translations from the web, then you can find them besides the lessons. To the right of the lessons you find "Real German from the web" with one or two possibilities for translations. Just click on them and you should see the sentences.
Sometimes you might see "You currently can’t contribute here." written there. That probably means, that for some reason there is no web content to translate available now. Then either wait or look in the other sections.