If you choose to give creator credit to download an icon for free, then you need to follow these requirements:
The format should be “Icon name” by Creator Name, from the Noun Project. The icon name must be hyperlinked to the original source. If you can’t hyperlink in the medium you’re using the icon, then type out thenounproject.com as the source. This attribution must be listed next to the icon, below the icon, or somewhere on the project you create to properly reference the icon.
To make it easier, free downloads include a line of text with the creator credit. However, if you would like to credit the creator in a different way or are using the icon in a different medium, you can copy the line of text and place it where it's relevant. Please see medium-specific credit requirements for more information.
Example 2: “Tree” icon by Edward Boatman, from thenounproject.com.