Out of the hundreds of different features Google Analytics has, the most valuable one (and easier to learn) is Advanced Segments. By segmenting your traffic you can learn how people use your website and make the most out of your marketing. For example, you could see that your Google traffic has a conversion rate twice as high as Twitter’s. Or that traffic from the UK is performing really well for you. That way, you can invest more in Google and the UK market, and less on Twitter.
I did this short video explaining how Advanced Segments work. Have fun watching it!