Woah! At first this may seem overwhelming. When you understand the basics, it all comes together. Plus, there are plenty of Android and iOS and Desktop options for software that makes understanding and applying for airspace approval a breeze.
If you plan on flying in an area with no automatic authorization, and there is no phone number listed in Airmap, please use SkyVector, which is more in-depth since it includes the aeronautical charts and a list of airports with detailed information on each airport. Best practice is to call the airport manager first before calling the tower directly. Contact info can be found in the airport chart supplement and ownership info. Please see this example.