I am near the beginning of my Dutch lesson and the very first question asked me to translate "to read" (spelling it out). I guessed correctly because I speak German but there was nothing in the previous lessons explaining the new vocabulary. Is there some kind of pre-reading I was supposed to do? Thanks in advance.
No pre-reading required, but it depends in which form you use Duolingo. If you use the app (on iOS or Android) it doesn't include any grammar.. If you use Duolingo on their website (which is more comprehensive) you'll see a Tips & Notes section when you begin a new lesson unit. This gives you a basic grammar explanation about that particular unit. I hope this helps you. You can use your same log in information for both the app and the website.
As an addition to Dutchesse722's useful comment, do note that there are occasionally mistakes where they don't realise you haven't learnt a word. The Dutch tree is generally really good and this doesn't have often at all. Sometimes you've got to take a hit because of a small bug and get the question right the second time around, it's not much additional effort.
The French tree is a different story, it seems very common for me to be translating words I haven't learnt on there.