I am hearing 'och' as 'o'. Are the c and h silent or is it my bad hearing/understanding?
You're right, och is usually pronounced just o. The k sound can be heard sometimes, e.g. if people try to speak extra clearly.
They're not the same – the girl = flickan = la niña but a/one girl = en flicka = una niña.
Did anyone else translate "en" as " an" and then it was marked incorrect? Sorry, but, on my account I hovered above the " en" and typed " an" because it says to say that...
In English, words that start with a vowel are always "an", like "an apple", whereas words that start with a consonant are "a", like "a banana". Duo is pretty strict on this, so you need to pick the right hint.
things that start with a vowel sound but there are exceptions to the above examples, when the vowel (u, eu, e, o) sounds like a 'y' or 'w' sound e.g A euro, a one legged race.
an is also used when the 'h' is silent: an hour, an honest person, OR with an acronym when the first letter is pronounced starting with a vowel, - an FBI agent (eff = F). Hope this helps too?
Contextually. It's usually a/an but if it's the counting version it's usually pretty obvious. :)