When you open ibis paint. Click on my gallery then the + button on bottom left. You’ll then get this screen…
Choose a canvas size. Then on the bottom left you’ll see either the paint brush or eraser …
Use the eraser to delete anything from a background. You can also use the magic wand tool but this is only suitable for deleting white backgrounds. Click on the number in the white box on bottom right. This is your layer tool. Change the background to the grey and white checked before you save and this will save as a transparent PNG.