This summary is not the rule. The rule text controls.
When the Supreme Court decides a case, someone has to make it official by writing it down in the court's records. This rule explains how that happens. The Clerk of Court takes care of preparing and signing the judgment, then entering it into the docket, which is the official record of what happened in the case.
If the court wrote an opinion explaining its decision, the Clerk enters the judgment after getting that opinion. Sometimes the exact wording of the judgment needs to be worked out first, and if that's the case, the Clerk waits until that wording is finalized. If the court makes a decision without writing a full opinion, the Clerk follows whatever instructions the court gives instead.
Once the judgment is officially entered, the Clerk must send a copy of both the opinion and the judgment to everyone involved in the case, and this has to happen on the same day the judgment gets entered. This way, all parties know right away that the case has been decided and can find out what the ruling means for them.