Legal Question in Family Law in California

It can be either, depending on the type of Stipulation and Order.

No, it's not a letter. It is drafted on pleading paper, in a format that complies with the California Rules of Court.

There is a court form for a stipulation and waiver for paternity cases, for waiver of final declaration of disclosure in divorce cases, and for some alternative dispute resolution matters. But you are not clear what you want to stipulate to, or for what kind of case, so I cannot tell you positively whether there is a court form for what you want.