Website owners pay a person to use their websites and give them a feedback so that they can make their sites user friendly.
Sites like userTesting.com, which provides quick and cheap website usability testing facility for site owners, offers you opportunity to earn some money. You have to become a member of their panel of testers.
To become a tester you must be at least 18 years old. You must have a computer running at least Windows XP, a broadband Internet connection, and recording facilities. Then you fill a one-page form with your demographic profile and your experience with computers etc.
Then download specific software which facilitates you to record a video of what is happening on your screen, mouse movements, clicks and key strokes, and your verbal comments while you use the website you are testing. You are asked to answer four questions on your experience of testing the website. The questions are: What would have caused you to leave the site? What ideas do you have to improve the site? What did you like about the site? Do you like to say anything else to the site owner?
You should, however, understand that website testing is not a get-rich-quick scheme. You cannot make it your career because you may not get sufficient work opportunities. You get offers only when your demographic profile matches the target audience of the site under test. Your success depends on your ability to provide useful feedback to site owners.
The main reason for not having sufficient opportunities for anyone to make website reviewing a career is that there is already an oversupply of testers.