"He or she is good."
Translation:Li aŭ ŝi estas bona.
Yes, it's not a vowel, it's a diphtongue. https://en.wikipedia.org/wiki/Help:IPA_for_Esperanto
"Li aŭ ŝi bona estas" is correct, but unusual. Word order is very flexible in Esperanto, but that word order is unusual enough that the course didn't accept it. "Bona estas li aŭ ŝi" would also be correct, but you'd be more likely to find it in poetry than in course for beginners.
After some research, I think that it has to do with what type of adjective this is, and in this case is a predicate adjective. Predicate adjectives (eg "La knabo estas bona.") always seem to follow the verb as it could otherwise be confused with an attribute adjective (eg "La bona knabo." aŭ "La knabo bona"). In my version of the sentence, bona would be translated as "good she", which in this case is clearly wrong.
It might be good, being forced to practice with the bubbles.
In Swedish there's a bunch of little accents, and not until recently I would just type the normal form of the letter (without the accents) which makes it harder to remember which word has the accents. And being that accents can change the entire definition of the word....
The word is "bona" with the adjective ending -a. The word "bono" does exist, but it's a noun meaning "goodness" or "the good". So it's really not a word you need to worry about at this moment. Stick to "bona" and you'll be OK. The plural is "bonaj". The main point is that in Esperanto nouns (names of things) end in -o, and adjectives (descriptive words) end in -a.