You still have to cite items you find in the Creative Commons. In fact, one condition of all CC licenses is attribution. For citing items from the Creative Commons, refer to their "Best Practices for Attribution" page.
This work, "90fied", is a derivative of "Creative Commons 10th Birthday Celebration San Francisco" by tvol, used under CC BY. "90fied" is licensed under CC BY by [Your name here].
The Creative Commons search is through Openverse. The tool allows you to search for images, music, video, and other media that have been given a Creative Commons license or are in the public domain.
The Noun Project is a place to find free icons. After creating a free account, you can use almost all icons for no cost, but you must give credit to the creator on the image. You can also purchase royalty free icons for $1.99.
This is a very good place to find minimalistic, but high-impact, images.