First of all, you need to get your bitcoin wallet. There are a number of solutions you can find information in this forum, but the general consensus is:
- a software wallet (desktop or mobile version) for smaller amounts
- the hardware wallet or "cold storage" for larger amounts, i.e. better safety.

After that, you will be able to create your unique addresses to receive payments.

When you want someone to pay you in bitcoins, you just send them your BTC address (or publish it on your website) and wait for funds to be available on your wallet. Only then you deliver your art works to them.