I want to type a label or information on the screen, how do I do that?

As AirGraph says, using a title would be the easiest way to write information on a slide.

You could also do it with text transparencies. So, you would make a duplicate of any random photo, then open it in the Preview app on your Mac. In Preview, do an Edit/Select All, Edit/Delete. That leaves you with a blank transparency screen. If a prompt appears asking if you want to convert, say yes. Then go to Tools/Annotate/Text and type a text on the screen. You can chose the font, color, and size from the toolbar at the top of the Preview screen. Save and import into iMovie. Overlay the transparency clip onto your video clip in the timeline, with the Picture in Picture feature. Adjust the size and position of the text on the screen. Then click on the blue Reset button to apply your changes.

-- Rich

Hello,

You can try to use Titles.

Do you mean something like a watermark that is always on the screen?