Meanings
colloquialdown, down here, downstairs (towards the speaker)
Er kommt jetzt runter. -- He's coming downstairs now.
colloquialdown, down there, downstairs (away from the speaker)
Er geht runter zu den andern. -- He's going downstairs to the other people.
Examples
GermanEnglish
Und dann ging ich runter in die U-Bahn.Then I went down into the metro.
Runter von meinem Dach!Get off my roof.