firstly, what are PNGs exactly?
basically, they are images that are transparent. as in no background. when you search on Google, search something like (object) PNG/transparent.

example :
they have a checkered background to indicate that they are transparent

but you can't find PNGs for everything you want, so here's how to cut out your own. on PicsArt.

get your picture you want to cut out.
METHOD ONE::
use the cutout tool

choose the brush size that's suitable and briefly trace around the model and press →

after it fills in most of it, though it isn't always accurate.

here, you can use the brush to refine and use the eraser to erase unnecessary things

once your done, tap → and it will automatically save to your stickers so you can use next time.

use if you want.

I saved it privately, but it still shows an apply button so when you wanna use it, you can tap that, and it lets you select your background. if not, just click add sticker and go to my stickers once you are already done your background.

you also just go to add photo while you are working on your cover and do the same thing.

now here's
METHOD TWO
the free crop tool.

you can use the brush and fill everything yourself but like why? instead, use the dotted line thingy.

with this tool, trace the outside of your model, carefully in one go. it then fills everything inside.

do some quick refining and you're done! it will save automatically in your stickers.

✖_✖
rip my gallery again. hope that helped. plesssss comment what I should do next. it helps a lott