iMovie lets you create movies from photos and videos, and while its interface is a little hard to understand in parts, you can overcome those limitations and master it to produce great results. But it has a few missing pieces that typically require you upgrade to something like Adobe Premiere Elements or even Final Cut Pro X or Adobe Premiere Pro CC.
One of those is adding text that overlays an image or video. Yes, iMovie has titles that you can add, but they are highly restrictive. Despite a large number of options, they’re difficult to control, including where you place them on screen.
There’s a low-tech/high-tech workaround that lets you use other Apple software to achieve titling results: Combine Keynote with iMovie and you can make your own text overlays, as well as intertitles and other titling cards. Why Keynote? Because it’s designed to make individual slides in the same 16:9 widescreen proportion used by iMovie.