That's easy all you have to really do is just go on to Poptropica and really if it says sign up at the bottom then all you have to do is think of a user name and password that you will memorize of course. That's how I got on Poptopica.
Go to www.poptropica.com than it says sign up than you click that and you do what it tells you to do
When I signed up for Poptropica, first I made a character, started to play, and when I was done playing, I clicked Save and Quit. The site then prompted me to make a username and password.