Operating privileges are based on license classes granted by the FCC. All exams are based on a question pool system, where all possible questions are released by the ARRL.
ARRL Resources: http://www.arrl.org/getting-licensed
Technician - Entry level exam. Privileges to most frequencies above 30 mHz. Limited HF frequencies
General - Given some operating privileges on all Amateur Radio bands and all operating modes.
Amateur Extra - Given all operating privileges on all Amateur Radio bands and all operating modes.
https://hamstudy.org/sessions (Online)
http://www.arrl.org/find-an-amateur-radio-license-exam-session (Local Area)