If you want to use the new feature of getting the location of your airport from the simulator you need to be connected to it before you start.  Open the sim and place your user aircraft at the location you want for the reference point of your new airport.

If you have the option set to auto connect to the sim then you will not need to have another project loaded before you can create your new airport.  ADE will automatically connect even if there is no project loaded

If you have manual connect as your connection method then ADE won't be able to connect until you have loaded a project.  So load any project and click the Connect button

Once you are connected you can open the new airport properties dialog from the file menu

If the Get From Sim button is not active then ADE is not connected to the sim.  If you want to connect then Cancel this dialog, connect to the sim and open the dialog again.  Of course if you want to enter the coordinates and altitude yourself you do not need to connect and you can just enter the data yourself.

1. If you are connected to the sim then this button will be active and you can get the location data by clicking it
2. Enter the airport details for your new airport
3. Click Save to create your new airport or
4. Cancel if you change your mind

Once you have all the information entered, click Save to create the new airport and load it into ADE

If you try to use an airport ident that is already used by  a stock airport then you will get a warning and will not be able to save the new airport until you fix it.  You may also get errors if you leave out the other airport identification information.

As soon as the airport is loaded into ADE be sure to save it.

You might also want to check that the project properties have been set up correctly for you.  If not you can change them for this particular project.