"I live in Tokyo."
は is used in either of the followings
To mark a noun as the subject of a phrase. が can also be used.
To mark a clause as a topic and stress the later part of a phrase. This is most common when the sentense is negative or a question.
In this sentence, the subject is わたし which is omitted. Also, the speaker does not want to stress anything. Therefore there is no は visible.
I see, so without the は The sentence starts with Live in tokyo, and the は exists in the case that you want someone to pay attention to the end of the sentence.
In English we begin the sentence with I "don't" but since the negative comes at the end in Japanese you're being told that important info will follow. It doesn't mean something as its own word, so much as it is a sort of punctuation.
住んでる居ます is wrong and cannot happen; it should be 住んで居ます instead.
However, it is customary in modern Japanese to write auxiliary verbs in kana only : 住んでいます
(In addition, for the verbs 居る and 有る, even when used as the main verb, it is much more common to see them in kana : いる and ある)
I happened to write:
That is, with -ます at the end instead of -います. However, Duolingo accepted this as correct!
If both 住んでます and 住んでいます are valid - is there a difference?
I think it's because に is used to describe a place in which something exists while で is used to describe a place in which an action is being done. Since it says that you live in Tokyo, you are existing in Tokyo, so you use に. If you were to say that you were working in Tokyo, you would use で.
This article might help you understand a bit! https://www.wasabi-jpn.com/japanese-grammar/japanese-particle-ni-clear-up-all-doubts-you-may-have/
Depends on your keyboard. If you are typing English characters which your keyboard software converts to hiragana, try typing xyo instead of just yo. If your keyboard has よ on it, type that first, then afterwards press the modifier key. On my android phone, I press よ followed by the dakuten/handakuten (ﾞ/ﾟ) button to get a ょ. I'm assuming the underline is just Duolingo's way of telling you that you can click on the character for more details.