You can use the content you create with us in a variety of ways depending on your needs. As a Free user, you need to leave untouched the Piktochart watermark. As a Pro user, you own the rights to your creation so you're free to publish or download your visual without the watermark, and use your creation commercially.
For a PRO account, any template selected and modified will not include the Piktochart logo when downloaded, published or shared. You may choose one of the PRO templates or one of the free templates and the final visual will not have any reference to Piktochart.