This summary is not the rule. The rule text controls.
If you want a jury to hear your case, you have to formally ask for one following the court's process. If you don't make this request the right way, you give up your right to a jury trial, even if you originally wanted one. Instead, a judge alone would decide the case.
Once you've properly asked for a jury trial, you can't just change your mind and cancel that request on your own. All the other parties who are part of the case have to agree before the jury demand can be pulled back. This rule exists to keep things fair and predictable, so one side can't back out of a jury trial at the last minute without everyone else agreeing to it.