Cut image or print-then-cut image?
A cut image throws the colours away. Whatever survives background removal becomes one flat shape, cut from a single sheet of vinyl — which is what you want for a logo, a silhouette or lettering.
A print-then-cut image keeps every colour, prints on your own printer with registration marks, and the machine cuts around the outside. That is the route for stickers and anything photographic. It has a size ceiling, around 6.75″ × 9.25″ on most Cricut machines, and wants at least 300 DPI at final size, so a small web image blown up to 6 inches prints soft.
Why the cut edges look ragged
Because the outline was traced rather than drawn. Design Space follows the boundary it detected between your artwork and the background, and on a JPG that boundary is fuzzy — JPG compression smears edge pixels, so the trace wanders in and out and the blade follows every wobble.
Two things fix it. Start from a PNG with a genuine transparent background rather than a JPG with a white one, so there is nothing to detect in the first place. And for anything you will cut more than once, use a real vector: an SVG carries the path itself, so there is no guessing and no wobble at any size.
Uploading from a phone or tablet
The iOS and Android apps have the same Upload button in the left-hand panel, and they pull from Photos or Files. The flow is identical: image type, background removal, cut or print-then-cut.
The one thing phones handle differently is archives. A design bought online usually arrives as a ZIP, and neither app can open one — on iPhone or iPad, save it into Files and tap it once to extract a folder, then upload the file from inside that folder.
What you are allowed to upload
Uploading is free and always has been. Cricut Access covers Cricut's own image and font library, not the upload button, so nothing about bringing in your own artwork requires a subscription.
Copyright is the real limit. A character, a team badge or a brand logo pulled off the internet is still that owner's artwork after it has been through an upload and a trace, and a licence for personal use is not a licence to sell. Designs from this library carry a commercial licence for physical products on a paid plan, which is the difference between a shop and a takedown notice.