By default all new users start with the free subscription plan. It gives access to most of the application functionality. Free subscription users have access to 1/3 of the storage space and 1/3 of the graphical content (fonts, images, cliparts and brush sets).
Free users get more than enough content and storage space for creating great graphics and buying merchandise. We are offering a huge amount of built-in content, so even 1/3 of it is enough for the needs of most people. As far as storage space goes, free users can probably create 5-30 projects, depending on how much space is consumed by images on the projects. It is actually possible to use all available space (currently 250 megabytes) in 1 project, but that would be very uncommon and should be avoided.
You need to go Premium to have access to the full server storage space and full graphical content. It's only $29 per year.
When you sign up, there is a subscription page under “My Account” page, that explains all this.