Creating trigger with after insert or update

[VirginiaT]

Hi everyone,
I am new to this forum and I am looking for some help. I am trying to create a trigger. What this trigger is suppose to do is after a user insert a record or update a record I need to add a date into a column in the same table. I have heard about mutating tables on a trigger with a before insert but will this happen on an after insert or update? Can anyone give me a simple and easy example as how to do something like this?

Thank you very much for any help I can get,
Virginia