It's sort of like Kickstarter for everything, I believe. Whenever you post stuff to Patreon, subscribers automatically pay an amount of money of their choice for the content that you post. People can subscribe for $0.00 or $1,000, any amount of their choice. The content creator can set up milestones/rewards for their subscribers!

Not sure how artists use it asides from stuff like funding for a tablet, or comics.