You can:

•  Use in any digital graphics you create for personal or commercial use, no attribution required. (eg. Social media graphics, ads, blog/website images, presentations)
•  Print and sell as part of a final product, as long as the graphic is modified in some way.
•  Use graphics on a book cover or within the book.
•  Use graphics in a design template that is for sale online.
•  Use as part of a logo for your company or use one of the icons in your logo.

You cannot:

•  Resell photos or icons as your own.
•  Sell unaltered copies of a graphic. (eg. Sell an exact copy of a stock photo as a poster, print or on a physical product)
•  Use images with identifiable brands to create a misleading association with a product or service.
•  Attempt to recreate an icon or stock photo site, using graphics found in Stencil.