It largely depends on what they're expecting. The position could range anything from executing manual tests to setting up and running a continuous deployment infrastructure and coding tests to run against every commit. As you're on HN, you probably want something like the second.

I started as a Test Automation Engineer about a month ago, and I'm using Selenium to write tests for all sorts of things -- do password changes work? Does the logout button work? Can a user edit another user's profile? Selenium is proving to be incredibly versatile. Grab it and try it out. Create your tests as actual code; don't rely on Selenium IDE.

Feel free to message me (email in profile) if you have any questions.