As of July 23, 2019, recreational flights in the US that occur within controlled airspace ( generally speaking, airspace within 5 miles of an airport or the areas under the red and green grids in the following image ) are required to get authorization using a system called LAANC. LAANC stands for Low Altitude Authorization and Notification Capability and is supported by many, but not all airports. As of May 16, 2019, recreational UAS fliers no longer have to notify anyone if they are flying in uncontrolled airspace.
As you can see in this image taken from the FAA’s UAS Facility Map, the airports with LAANC are highlighted in green while those without are highlighted in red. To obtain permission to fly recreationally in the green areas, you can do so with an app on your mobile device.
At this time there are two apps available that offer LAANC for free. Those two apps are Airmap and Kittyhawk. Using one of these two apps will allow you to request and potentially receive near instant authorization to fly in controlled airspace up to the altitude displayed on the map. For example at the farthest edges of the green grid you can see the number 400. That means LAANC can authorize you to fly up to 400 feet in those areas. Near the center of the controlled airspace you will find grids with 0’s in them. LAANC can not authorize you to fly at all in those areas as the maximum altitude you could fly would be 0 feet.
For detailed instructions on using either Airmap or Kittyhawk to make a LAANC request, take a look at their recreational LAANC users websites linked below.