You're right in thinking that it refers to ‘people as a tribe/community’. In this case, ‘a people’ means ‘the entire group of people (that usually has something in common e.g. language, culture, ethnicity etc)’.
I recently read the first chapter in The Cambridge Encyclopedia of the English Language by David Crystal and came across the same usage of ‘a people’...
It depends on what you try to convey.
If you talk about your handstand routine, progress, work, you can say "my handstand". If you talk about the exercise, the pose, the technique in general, you can say "the handstand". "A handstand" refers to one instance of this exercise, a repetition. "Do a handstand" is the usual ...
This is actually a fairly common idiom in English, especially in advertisements and news articles. The implication is that the product is not unique---perhaps a new version every year, or perhaps it has been revamped. But this is often applied to people as well. Consider this print title:
"A New Donald Trump? Moving Holocaust Speech Wins Praise From ...
Yes. Here's why.
Where conversations involve more than 2 people, and articles are used, use of the means everyone should know which X, and those that don't will have to ask questions to catch up, or just remember that you don't know which X and need to pay attention to get that information when you can.
In fiction, sometimes the conversation includes you as ...
It is normal to say "by post" in British English (or "by mail" in American English).
You would never use an indefinite article with "post" in this context, since there is only one post ("a post" would therefore be a fence-post or similar). However, it can be correct to use a definite article, as in "through the ...
No, by here shows the method in use, how the action of sending documents is done - by post. It's an uncountable noun which refers to the public system for collecting and delivering of letters, so a post is never the case.
Similarly, you can travel by train/car, you can pay by cheque, you can carry/ship goods by sea/air, you can read by candlelight.
We use ...
On the broader point, adjectives are partitive. Green apples are a particular type of apples in the category of all apples. Green apples are part of all apples.
The same thing applies with uncountable nouns.
A little/deep/good/wide/slight/simple, etc., knowledge.
Zest = the entire category of things that can be described as "zest".
Certain (adj.) = ...
A fire (countable) is any instance of fire. It can be a building fire, a forest fire, even a campfire. If it's too small (e.g. a candle) it's probably better referred to as a flame, but in general, instances of fire are easy to count and are well-defined in their extent and duration.
In your example, whether "fire" should be countable or ...
For example, wind and fire are countable and uncountable.
It is dangerous for children to play with fire. [uncountable].
A fire destroyed my kitchen last year. But the fire did not destroy the rest of the house. [countable]. House fires can be devastating to families.
A cold wind blew all night long. Now, there is no wind at all.
Wind is needed for sailing. ...
They are both correct.
In this version, we expect to be told about the fire. For example, "The building was destroyed by a forest fire."
Here we might assume that the source of the fire was within the building itself and the fire was probably restricted to the building.
The above is not an inviolable 'rule' but it's a good guide.