Oke, last time I posted I asked about creating a trigger. Now I have the next problem. I'm trying to create an automatic patientnumber in the next view.

CREATE VIEW V_PATIENT AS
SELECT PATIENTNUMBER
, FIRSTNAME
, LASTNAME
, STREET
, HOUSENUMBER
, POSTALCODE
, CITY
, PHONENUMBER
, BIRTHDATE
FROM PATIENT;

I created the next sequence:

create sequence autonummer
INCREMENT BY 1
START WITH 1
MINVALUE 1
MAXVALUE 999999999999999999999999999
NOCYCLE
NOORDER
NOCACHE;

What I'd really like to know is how I can use this sequence in a trigger to create an automatic patientnumber.

Sequences are nice to use for auto-generating PK values for new
record inserts or, possibly, in your case for generating a "patient
number". Here again, though, this would be used for new record
inserts only. To see the current sequence value, use .CURVAL; to
obtain the next value, issue .NEXTVAL.

The view your displaying, I guess, is to display those records that
exist in the database. Consequently, the view does not access the
sequence but rather references the table column represented by
the "patient number".

Well, it is my intention to create an automatic number each time a new patient is inserted. My guess is that it has to be done with a sequence like the one above.
I can get it to work if I use

insert into v_patient
values (autonummer.nextval, firstname,.........);

But isn't there a way that oracle does this automatic everytime there is a new patient ( i don't want to type autonummer.nextval every time I insert a new patient).

You can do this with a trigger, something like this:

The trigger gets the next patient number from the sequence when you insert into the table with the patient number omitted.