Something like this should get you most of the way:
create TRIGGER [name] ON
FOR INSERT
AS
update
set created_by = SUSER_SNAME(),
last_modified_by = SUSER_SNAME(),
date_created = GETDATE(),
date_last_modified = GETDATE()
from inserted
where
.Seqno = inserted.seqno;
create TRIGGER [name] ON
FOR UPDATE
AS
update
set last_modified_by = SUSER_SNAME(),
date_last_modified = GETDATE()
from inserted
where
.Seqno = inserted.Seqno;
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.