This summary is not the rule. The rule text controls.
If someone testifies about a statement made outside of court, and that statement is being used to prove something is true, a judge normally won't allow it as evidence. This is called hearsay, and the basic idea is that courts want witnesses to speak from their own knowledge, not repeat what someone else said.
There are plenty of exceptions to this rule, and other laws or court rules can allow certain out-of-court statements in. But unless one of those exceptions applies, hearsay stays out of the case. This matters because it affects what a witness can actually say on the stand and what evidence a judge will let the jury hear.
