I would be careful using
Browser uses it.
If your going to learn Selenium I would focus on the
learning the WebDriver API (Selenium 2.0+) as this is where
all the development effort is going within the project.
I would recommend avoiding xpath where possible for
finding "elements" within a web page for two reasons:
1) xpath lookup performance using IE is very very bad
2) xpath lookups can be very brittle, just adding a
single additional html element to page can often
be enough to the stop the xpath lookup
Looking at the Groupon page they use a good amount of
element id's and CSS classes within their HTML, so using CSS
selectors to find elements should work well.