I Want To Sell My Own Printed Tshirts Can Someone Assist Me

I want to design and print my own t-shirts made and sell 'em. Does anyone know a place (website or Even Better) That prints and sell in wholesale? Also, Is There Anything I need to worry about? If Someone has experience in customizing and selling shirts, can you assist me please?

Btw, I'm Not Trying to start a business, just wanted to make a few "spare extra bucks on my free time.