The Technician Class is where most Hams begin. This class allows you to work on the VHF and UHF amateur radio frequencies. Modes include voice (FM & SSB), Morse Code, and digital modes. All that is required to attain this license is the passing of a written exam.
With the General license, you are allowed the use of all modes and bands in the amateur spectrum except for a few small band segments reserved for the last class.
The Extra class is the highest amateur radio license you can obtain. The written test is the most difficult of all the license exams. With this license, in addition to the privileges allowed by the other classes, you are allowed the use of a small segment of each of the HF bands that is set aside specifically for Extras.