Unregistered users have full access to the database via the search form at the top of the page. Registered users can also search the database via an advanced search form that is easy to use and that provides lists of values that are contained in the database, e.g., a list of countries so you don't have to guess whether you should search for "UK" or "U.K." or "United Kingdom" etc. They can also use the group-by function which provides statistics.
We didn't make the advanced search accessible for unregistered users, because we want to encourage users to register. Registration provides means to us to gather some information about our users, which can help us to improve Outbreak Database.
Of course, all your data will be treated confidentially.
Most likely your browser is blocking the Captcha image. You could try to register with another browser or on a different computer.