"Mám jednoho bratra."

Translation: I have one brother.

[MargaretWaddell]

My problem is that we didn't learn this before being questioned on it. I guessed wrong.

[VladaFu]

In Duolingo you learn by practice. That is the whole point of Duolingo.

[AgnusOinas]

If you don't know a meaning of a word or its translation, you can hover your mouse over it (web) or tap it (app) to get a hint (or pretty much the solution). This is especially useful when you see a word for the first time.