This summary is not the rule. The rule text controls.
If you want to ask the court to do something in a criminal case, you have to file a motion. A motion is just a formal request asking the judge for an order or a decision on something. Anytime someone wants the court to act, this is the proper way to make that request.
Most motions need to be in writing. The only time you can skip this is if the motion comes up during a trial or hearing, or if the judge gives permission to make the request out loud instead.
Whether written or spoken, the motion has to clearly explain two things: why you're asking for this (the specific reasons or legal grounds) and exactly what you want the court to do about it. You can't just say the other side did something wrong. You need to spell out the details and state the outcome you're asking for.
Finally, you're allowed to back up your motion with an affidavit. This is a written statement, signed under oath, that supports the facts behind your request. It's not required, but it can help show the court why your motion should be granted.