This summary is not the rule. The rule text controls.
A grand jury doesn't have to wait around for someone to tell it what to do every single time. The court can schedule a meeting, but the grand jury also has the power to call its own meeting if at least nine of its members agree to it. These meetings can happen anywhere within the parish, not just in a courtroom.
For the grand jury to actually do business, at least nine members need to be present. This is called a quorum, and it's the minimum number needed before any official action can be taken.
When it comes to indicting someone, meaning formally charging them with a crime, at least nine grand jurors must agree. Even if more than nine are present at the meeting, the charge only moves forward if nine or more vote in favor of it. This rule makes sure that a strong majority of the grand jury supports any decision to charge someone with a crime.