Legal Question in Civil Litigation in California

You can do both. But very few hearings (depending on the type of case) allow for witness testimony.

Mr. Selik beat me to it. Usually, judges won't take live testimony for a hearing in a civil matter. The exceptions that I've seen involve motions to quash service. Then, the process server will testify about how the summons and complaint were served. If it's any other kind of motion, usually, evidence is presented as part of the moving or opposition papers by way of a declaration signed by the witness under penalty of perjury.

For trials, a witness needs to testify and a subpoena should be issued and personally served, unless it's for a friendly witness (or a relative), who volunteers to appear at trial. Even in those instances, it might be best to issue a subpoena to make it official, in their minds, that they have to appear and will have second thoughts about having cold feet.

You got technically correct answers. The real answer is that if you can't figure it out on your own, you either hire an attorney to help you with your case, or you lose it. There are some people who are not lawyers who can handle a case in pro per against another pro per party. Someone who has to ask as fundamental a question as yours sooner or later will not only lose their case but will do so in a "handed your hat" level of embarrassment. I am not saying this to be insulting but simply to warn you that you are headed for a cliff and once you are over it your legal rights will be lost forever.