I've seen plenty of people making commissions with your level of skill.... Looking through your gallery, it looks like the most popular pieces there are lined by another artist and you've done the colors. If you're only offering colors, just make sure it's clear up-front that the person requesting the commission needs to supply the line-art.
I can't really offer advice on setting up PayPal in particular. I know PayPal is a bit different in other countries because they have to conform to the local banking laws. But the basics should be the same - you have an email address you sign up with and then once you have your PayPal account, people can send you payments through that email address. You may have to manually convert from US dollars if people want to pay you in US currency. Someone recently sent me $5 in Canadian currency and it's sitting in my PayPal account labelled $5 CAD because I haven't converted it to USD.
Good luck!