The following list of links are for you to read and learn from. There is a ton of infomation in these links which will give you a good understanding of civil and military air monitoring. You will also find alot of frequencies in these pages, both vhf and uhf pertaining to civil and milair listening. So plug them in and get started listening. Most of these links are from the Radio Reference Wiki.

Aircraft Monitoring

Military Air Monitoring

ARTCC (Air Route Traffic Control Center)

HF Military Monitoring

Finding Air Traffic Frequencies