AdWords is Google’s ad-selling system, where advertisers pay money to advertise on Google, or on individual websites. You need an AdWords account for unlimited Google Analytics so, if you eventually want to advertise for your website, you can jump right in. However, you do not need an AdWords account if you have less than five million monthly page views, just a simple Google/Gmail account.
Haven't you heard of Wikipedia too? http://en.wikipedia.org/wiki/AdSense http://en.wikipedia.org/wiki/AdWords
Make is simple, adsense is PPC advertising program for the publisher and adwords is PPC advertising program for the advertiser