If you are thinking about graduate school in the united states, writing the GRE is usually required. Find out more at the official site, or from other third parties. Third party sites are often full of good summaries, but may be trying to sell you something so beware. For more advice, bring the GRE up with your adviser at your next meeting!
Want some help exploring careers in physics? try the SPS Careers Toolbox for Undergraduate Physics Students:
In 1952 a former department chair, Daniel Posin, published an interesting book (link) attempting to dispel certain public fears. It is as interesting now as it was then, but also serves as a useful window into the perceptions of the public in 1952. Have a look!