The ablative of means
This answers the question 'With what did you do that?', telling you the means by which or instrument with which an action is done,
The master beats his slave
with a book
which in Latin would be: dominus servum
pulsat libro.
This use of the ablative also expresses the agent of a passive verb when the agent is a thing and not a person,
The house was destroyed by fire
which in
Latin would be: domus igne deletus est
