This summary is not the rule. The rule text controls.
If someone gives their agent special permission, that agent can file a lawsuit on their behalf to enforce a right that belongs to them. This means you do not always have to go to court yourself. You can authorize someone else to do it for you, as long as you give them clear permission first.
Even though the agent is the one filing the case, the law still treats the principal (the person the agent represents) as the real plaintiff. This matters because the person being sued can use any defense against the case that they could have used if the principal had filed it themselves. The defendant is not at a disadvantage just because an agent is handling the lawsuit instead of the principal.
The defendant also has the right to file their own claim back against the principal, called a reconventional demand. This is similar to a countersuit. It lets the defendant raise their own legal issues in the same case, directed at the principal, even though the agent is the one who technically brought the lawsuit.