How do I add my own photos to screensaver?

Can someone point me to an article that explains how to add your own pictures or photos to SysPrefs/Screensaver in High Sierra? I remember I could do that in Yosemite, but I've forgotten how. (Saw an article saying Click on the + button in Screensaver. I found the + button for Desktop but not for Screensaver.) Thanks for any information!