If you are not signed in: You may get one complimentary watermarked preview. After that, sign in and buy Preview Credits to keep creating generating new artwork, or testing different styles and color palettes.
If you are signed in: Every new account gets one complimentary watermarked preview. Every other preview image uses Preview Credits from your account. If you don't have any Preview Credits, you will be prompted to buy them before you can make any new art.