Do you need to be paid if you help someone with background art?
No, not necessarily. It depends on yourself. If you are someone who has practiced art for a long time, you have experience, knowledge and people would actually pay for your art, then you could charge people. The people that usually charge are those who make a living off of that commission. However, if you aren’t experienced in art and people won’t pay you to make something of terrible quality, it’s best not to charge them.
How can I make my own backgrounds?
That’s really hard for me to explain especially as I’ve never done it before. I’d assume it was just mixing and matching free to use images in photoshop.