"The restaurant at the corner opens at 10."
あく is what we call the "dictionary form" of the verb. If you look up "to open" in the English-Japanese dictionary, you will find あく. You use the dictionary form for the present/future tense. All verb conjugations are derived from the dictionary form.
あきます is the "-masu form". It is used for the polite present/future tense. Duolingo only focuses on teaching the polite conjugations of verbs, as these are the most useful for talking to strangers.
Take a closer look at Japanese verb conjugation if you'd like to understand it further.