The Extra class license is the final level in the Amateur Radio Service.  It requires strong knowledge of electrical and radio theory as well as rules and regulations.  The exam is a written, multiple-choice test consisting of 50 questions.  Passing a 5-WPM Morse Code Exam (if not already passed) is required.  These do not need to be done simultaneously.  You can pass either test first and receive credit for it for later (Written Exam=1 year credit, Morse Code=Lifetime credit).

Extras have access to the the entire Amateur Radio Spectum.  This includes special segments of the Shortwave bands which are less crowded and offer more opportunities for DX (distant signal) contacts.  Extras also have all of the privileges offered to Technicians and Generals.
 
Extras may use AM, FM, Single Sideband (SSB), CW (Morse Code), and digital modes of communication as well as Amateur Television (including Slow Scan) in their allotted bands.  
 
There are several good study guides to assist you in your quest to be licensed.  Some of the best are:

What's Your Next Step?

Find an examination session near you and register .  Go take the exam.  Extra Class Operators have lots of HF privileges.  It can also be a good thing to put on a resume if you are looking for work in the communications field.