GIMP

Something like this, I found this on a example business presentation, and for my assignment I would like to create the same effect in gimp, making transparent jagged-edges for likely a image on the right, to look better blended with the slide on the left, how would I do that in gimp? I tried setting a alpha channel, and erasing parts of the image, but it only saved a small portion of the image as a png, and just look severely distorted as a jpeg. (Original image was webp, and I selected the option to fit the canvas over the layers). So if you have a idea on how to approach this (preferably a step-by-step guide), I would like to hear it