one
In French, 'un' is the masculine singular form of 'one'. It is used before singular masculine nouns to indicate that there is one of something. For example, 'un livre' means 'one book'.
A man is reading a newspaper.
In this sentence, 'Un' is used twice. Firstly, it is used to indicate 'a' before 'man' (homme). Secondly, it is used to represent 'a' before 'newspaper' (journal). In French, 'Un' is the indefinite article for masculine nouns.
I want a coffee.
In this sentence, 'Un' is used before 'coffee' to mean 'a'. So 'Je veux un café' translates directly to 'I want a coffee'. The phrase illustrates the most common use of 'un' as an indefinite article in French.
A black cat.
In this phrase, 'Un' is used before 'cat' (chat) to mean 'a'. So 'Un chat noir' translates directly to 'A black cat'. This sentence demonstrates how 'un' is used with masculine nouns.