N300 WiFi Range Extender Installation

HELP! I'm an "older" person who needs help to set up my N300 WiFiRange Extender. Under "Quick Start", I have the (1) Power LED on solid green; (2) WPS LED blinks; (3) My Problem: what/where is the WPS button on my router or access point??? (I am connected to WiFi through my Cable Company--don't have any idea what is meant by WPS button)