How do I delete "Click to add title" in Power Point?

Are you creating slides from a template, or creating a template?

When creating slides, clicking on the Click to add title text will delete the prompt text and you can start typing the replacement text.

When creating a template, you can set the wording of the prompt text by choosing View>Slide Master. The layout opens that is responsible to the selected slide. Select the placeholder text and delete it, or type in new prompt text in your preferred wording.