How are google & stumble similar? How are they different? What would you use each one for?

Google is a search engine for surfing the web, and stumble is a discovery engine that finds the best of the web. Google allows you to search the web, watch videos, and etc. StumbleUpon allows you to chat with your friends, connect to what you like (sports, music), and etc. I always use google for Facebook, for homework, and for YouTube. I haven't experienced a StumbleUpon because I made one yesterday.