Adverbials is used to give more information about a verb.
It can be used to express place (where it happens), time (when it happens) and manner (how something happens).
Example :
I met Diana in London.
I met Diana in December 2008.
I met Diana when we attended a conference.
(verb – met, Diana – subject, London – adverbials, December 2008 – adverbials, attend conference – adverbials)