This is the 6850th most frequent Swedish word.
one
The Swedish word "one" is not a word; it seems to be a typo or confusion. If you meant "en" or "ett," they mean "one" in English, used as numerals or articles.
Here, 'man' is used to mean 'one' in general, referring to people in an indefinite sense.
Man bör alltid vara vänlig.
One should always be kind.
Here, 'en' means 'one', which is a numeral indicating the quantity of the object 'book'.
Jag har en bok.
I have one book.
In this sentence, 'ett' corresponds to 'one', representing a single option out of multiple possibilities.