This bit is wrong:
"kommt" means "is coming"
At least if with “means” you mean “is exactly equivalent to, and can always be translated as”.
In this sentence, kommt cannot be translated as “is coming”, since we’re talking about origin, which is an “eternal truth”, not an action; we use the present simply tense for that in English.
Britain is England, Scotland & Wales, (excluding Northern Ireland as its part of the island of Ireland and while it is part of the UK it is not part of Britain,) so the reason it is "incorrect" is because what you said could be taken to mean she is coming from Scotland or Wales. But we know she is coming from England. I hope this is helpful. :).
In this context, yes.
When we are talking about the extraction or origin of something, we say 'aus'. Or else, 'from' is normally translated to the German word 'von'. For example: Es kommt aus Kopenhagen = It comes from Copenhagen (i.e. it's origin is in Copenhagen) Es kommt gerade von Kopenhagen = It comes straight from Copenhagen
'Aus' can litterally mean 'out', 'out of' or 'out from'.
German verbs conjugate based on who's doing them.
"ich komme" is "I come" and "er/es/sie kommt" is "he/she/it comes".
Here are all the conjugations of kommen:
ich komme - I come
du kommst - you come
er/es/sie kommt - he/she/it comes
wir kommen - we come
ihr kommt - you (as in several people) come
sie kommen - they come
Sie kommen - you (formal) come
The hover/tap hints are a bit like dictionary definitions -- words can have many meanings and not all of them are appropriate in a given sentence. (For example, "bat" can mean a wooden stick or a flying mammal, but playing baseball with a flying mammal wouldn't work very well.)
When asking about someone's origin, say "She is from England" or "She comes from England" -- that's not an action but a timeless statement, so use present simple, not present continuous.
"is coming" as a translation of kommt would be appropriate, for example, when literal movement is involved, as in "She is coming to visit us tomorrow." Sie kommt uns morgen besuchen.
the ending -t is singular and plural
The ending -t is specifically for er/sie/es (he, she, it) and for ihr (you -- several people).
So sie kommt cannot be "they come", because -t is not used for "they".
"they" uses the ending -en, e.g. sie kommen.
Do not think of verb endings as "singular" or "plural". Rather, associate them with specific subjects such as wir or du.
So is Sie, Er and Ihr all kommt?
That is correct.
er, sie, es and ihr both have verb forms ending in -t.
For some verbs, er, sie, es and du verb forms change the vowel (e.g. geben has du gibst, er/sie/es gibt but ihr gebt) and then the er, sie, es and ihr verb forms are different, but for the majority of verbs, they are the same (e.g. er/sie/es kommt; ihr kommt).
Why she is comming from germany is wrong?
- "comming" would be a form of the rare verb "to comm" = to communicate. The correct spelling for what you want would be "coming" with just one M.
- There is no word "germany" in English. Country names are written with a capital letter: "Germany".
- The German word England means "England", not "Germany".
- We use the present simple tense in English when we talk about someone's national origin, so sie kommt aus... is "she comes from..." and not "she is coming from...".
What is the difference between "kommt" and "kommst"?
Different forms of the same verb; you have to choose the one that matches the subject (a bit like choosing between "is" and "am" and "are").
-t is for er/sie/es, singular nouns, and ihr ("you - several people whom I know well").
-st is for du ("you - one person whom I know well").
Read through the tips and notes for the "Basics 2" unit again to refresh your memory of the verb endings for regular verbs: https://www.duolingo.com/skill/de/Basics-2/tips-and-notes