This is a great overview of what a/b testing is and why you should be using it. If you aren’t making user research + metrics driven decisions it’s like you are on a gun range in the dark shooting blind and no you don’t have night vision goggles. Whether or not you choose to use Optimizely, the company that gives the presentation is completely irrelevant.
Optimizely does however have a section on the site that explains A/B testing.
Mixpanel is another great place for getting started.
FYI – A great startuping resource
There are a lot of other useful videos for those interested in creating a startup on Google Venture’s Youtube Channel.