sie "she" (almost always) uses verb forms ending in -t: sie hat, sie trinkt, sie kommt, .... Some exceptions: sie will, sie weiß, sie wird, sie muss, sie kann, sie darf (no ending -- like how English "she will, she must, she can" have no -s ending).
sie "they" (almost always) uses verb forms ending in -en: sie haben, sie trinken, sie kommen, .... Some exceptions: sie sind (irregular), sie ändern, sie handeln, ... (no -en after -er or -el, just -n).
The two sie words sound the same but they have different meanings and they require different verb forms.
That's how German works. I'm not sure what kind of "reason" you're looking for.
It appears that German conversation is about context, so if you are speaking and you say "she comes from Germany," you would not know if she was born there without either asking for clarification, or the speaker said "Sie wurde in Deutchland geboren." Which is "born in," versus "comes from." How do you know the difference in English? Different vocabulary, different verb tense. For right now, though, "she comes from Germany." If you want to know more, you can have a conversation, engage, and ask the speaker for more details. Just my take on it but I too am learning.
It's both. "sie" can mean "she" or "they". You can tell the difference by the conjugated verb, as the conjugation for "she" (3rd person singular feminine) is different from "they" (3rd person plural): sie kommt (she comes) vs. sie kommen (they come).
To make it even more complicated, there's also "Sie" with capital "S". It is the polite "you"/"you all", i.e. singular and plural. The conjugation is the same as for "sie" meaning "they". "Sie kommen" means "you come". So if the "Sie" is at the beginning of a sentence, you can't tell if it means "they" or polite "you". But you still have context to deduce this.
I hope I could make it clear and didn't confuse you even more. If you still have questions, feel free to ask.
If it's the subject, you can tell by the verb ending -- sie kommen has to be "they come" because of the -en ending, while sie kommt has to be "she comes" because of the -t ending. (In the present tense.)
If it's the object, then you usually can't tell the difference between "them" and "her", except by context.
How do you get "They came to Berlin" out of Sie kommt aus Deutschland ?
That sentence says nothing about Berlin or about "to".
Also, sie kommt means "she comes" (third person singular, present tense), not "they came" (third person plural, past tense) which would have been sie kamen.
Are you referring to the capitalisation to distinguish the two?
Then that's not correct.
"she" and "they" are both sie, lowercase.
But since the first word of a sentence is capitalised (in German as in English), they will both look like Sie when they are the first word of a sentence.
In the middle of a sentence, Sie can be neither "she" nor "they"; it will be the polite "you".
You can tell by the verb endings:
- sie kommt with -t: she comes
- sie kommen with -en: they come
Similarly with sie trinkt/sie trinken; sie isst/sie essen; sie heißt/sie heißen etc. etc. -- the "she" form almost always ends in -t, the "they" form almost always in -en.
A notable exception is the verb "to be", which is sie ist / sie sind.
In the sense of "to", I believe that's true for all cities.
For countries, it's true for most countries whose names are neuter and which are used without an article, e.g. nach Frankreich "to France".
For countries with other genders (masculine, feminine, or plural), it's usually in, e.g. in die Schweiz, in den Sudan, in die Vereinigten Staaten.
For country names that are islands, auf ("onto") may be the correct one, e.g. auf die Malediven "to the Maldives".
In this sentence, of course, you're not coming to Germany but from Germany, and here aus is correct rather than nach
Why is they not acceptable
Seriously? biertopf and I (mizinamo) have answered this question multiple times on this page already.
Does nobody ever read the existing comments? Do you need a personal, private response?
Why do we even write these answers?
I always think that I'm answering not just that one person's question, but for everyone who might have the same question.
I was dinged for translating it as come/coming from.
I'm not surprised if it dinged you for using the continuous aspect "coming from" -- someone's national origin is a (more or less) permanent fact, and so we use present simple for that: Kommst du as Deutschland? can be translated as "Do you come from Germany?", though "Are you from Germany?" is probably more common.
But Are you coming from Germany? is not appropriate.