I would say 'I have had my breakfast this morning'. It would be a response to a question: 'have you had your breakfast already?' I could not use 'since' in the way you have, because 'have had' implies an event that already occured, and 'since' implies that is has been occuring all the time from then until now. Here are some other examples: I have had several bicycles in my lifetime, but this one is my favourite. I have had some time to think about your problem, and i may have a solution It implies possession, of a subject, in the past. if the subject is plural, the possession event is likely plural. I would not say 'I have had a bag of apples' - it would have to be 'i have had bags of apples' or 'i had a bag of apples' It can also be used as part of an idiom: I have had it up to here with your foolishess! (i am angry, you have reached the limit of my patience)

have had = Present Perfect fetch a grammar textbook and read the proper chapter