among
The German word "unter" is used to express the idea of being among or between things. It can be used in a variety of contexts, such as "unter Freunden" (among friends) or "unter den Bäumen" (among the trees). It is also used in the sense of being under something, as in "unter dem Tisch" (under the table).
I live under a bridge.
This sentence is using 'unter' in a literal sense to express the location of where one lives, which is under a bridge.
He sleeps under the stars.
Here, 'unter' is used to signify beneath or below something, in this case the stars. This phrase is expressing an activity happening under/beneath/below the stars.
We are among friends here.
'Unter' is also used to express being in the company of a group. This phrase, 'Wir sind unter Freunden hier,' suggests that 'we are in the company of friends here.'