This summary is not the rule. The rule text controls.
Before anyone testifies in court, they have to promise to tell the truth. This promise can be a religious oath or a simple affirmation, whichever fits the person's beliefs. The point is to make the witness understand how serious it is to tell the truth on the stand.
There's no single required wording for this promise. The court just needs to use a form of oath or affirmation that will genuinely remind the witness of their duty to be honest. This means the process can be adjusted to respect different religions or personal beliefs, as long as it still drives home the seriousness of testifying truthfully.
If you're called as a witness, expect to go through this step before you answer any questions. It's a standard part of every case, not something unique to your situation. Refusing to take an oath or affirmation of any kind could prevent you from testifying at all.