The cropper finds your face and starts the square around it, so a wide or tall photo becomes a good square in one go. Move and zoom it as you like.
Why square
Nearly every platform shows a profile picture square or round. If you upload a tall photo, the app chooses which square to keep, often the middle, which can cut your head off. Crop it yourself and you choose.
Questions
Is my photo uploaded?
No. The crop is made on your own device, in your browser.