GO to this website https://www169.lunapic.com/editor/
CLick “Upload” at the top left of the screen, then click the big blue “Browse” button on the middle right.
Once your pic is uploaded, then click "Edit"
At the bottom of the edit list is "Transparent Background"
CLick that, then click the white(or other colored) colour surrounding your drawing/image.
The white/colored background will be checkered to show it’s been deleted or transparent.
Then save the image.
When you upload or use the image, the white/colored background will no longer be there.
Also there’s this free app you can use (contains ads) to remove a background
Background Eraser - Cut Out photo to make PNG & superimpose by Alan Cushway
This is a bird i made with microsoft 3D paint.
The white background has been removed. SO if you copy/save this image, the image will just be the bird.
This is helpful if you like drawing your characters for games and don’t want a big rectangle sprite or the background.