Go to www.picnik.com. The site will show up like this. Press "Get started now!"
Step 1: Upload a Photo
There should be a button that says "Upload a photo". Click that button.
(It also greets you by saying "Hi, Guest! Welcome to Picnik!" And underneath that, it says "Picnik gets even better if you register for free." To create an account, click "register for free".)