How to make only relevant part of image appear on Davinci Resolve

DISCLAIMER: I'M NOT HIRING. THE POST EDITING PAGE FORCED ME TO ADD THE HIRING FLARE AND THE TEXT "Rate per hour 4" BECAUSE IT SAID THAT IT LOOKS LIKE I'M POSTING A JOB, WHICH IS NOT THE CASE

Hello, guys, sorry if this is too basic a question, but I'm quite new to video editing.

So in this tutorial

https://www.youtube.com/watch?v=AcNOi-PUTL4

at 30:30 Kevin includes an image of the logo for his cookie company and immediately only the relevant part of the image appears (i.e, the image does not appear as a square overlaid on top of the video).

I tried to do that with other images I pulled from the internet but it just doesn't work. You can see the entire picture, the "relevant" bit as well as the background, regardless of whether that background is black or white.

Does anyone know how to achieve what Kevin did in his video? Thank you.