We use Passive forms of the verbs when:
the doer of the action is unknown:
My handbag has been stolen.
The new house has been vandalised.
we want to focus attention on the action rather the doer:
The project was done two days ago.
The widows were painted yesterday.
we want to put special attention on the doer:
All these books were written by her.
We were told a new story by Sarah.
Passive Voice is more common for written and spoken English. It is also used in newspapers and by journalist.