What Flight Simulator version are you using, 2004, X, or other? Though the process is basically the same for each, the tools may differ.

The basic the steps are:
Flatten the area for your new airport using one of the 'flatten' tools.
Exclude default scenery objects and autogen objects using one of the 'exclude' tools.
Build your airport facilities (runways, taxiways, aprons, parking, communications and navaids)
Place 3-D objects (buildings, etc) using one of the 'object placer' tools.

The specific tools used, and how to use them, depend on which sim your using. Many  are available in SimV Downloads,  Utilities or Design Utilities sections.

Dave

Yes, Afcad is one of the tools you will use. It is used to place the visible parts like runways and taxiways and aprons, surface and approach lighting, as well as invisible stuff like runway and taxi routes, for atc and ai, and comm and nav freqs. It cannot place 3-d objects like hangers and such. In theory you can also flatten the airport area by drawing an apron. This is problematic as any apron you draw on top of that, for parking areas or such, will not show.

Flatten--is usually done using one of the utilities designed for the purpose. FlattEx is a small utility that will help you create 'flatten lines' to put in your 'scenery.cfg' file.

Exclude--FlattEx will also create the 'exclude lines, for the 'scenery.cfg' file, to remove default objects and autogen from your airport.

Building your airport facilities--Afcad

Place 3-d objects--Rwy12 is a freeware 3-d object placer. It will place objects from the (FS9) default  scenery object libraries as well as many custom object libraries created for use with Rwy12. (Download the program as well as the 3 object libraries.)

There are other programs/utilities available for these tasks, both freeware and payware, but these are probably the simplest to get you going.

Dave

Each of the tools  come with help files. It's best to read thru each before starting your first project. I would suggest printing the FlattEx and Rwy12 files out or a least creating a desktop shortcut to each (Afcad's help is available from withinin the program).

I don't know of any tuts specific to creating an airport with these particular tools. Reading the Afcad help file's section on 'Creating a New Airport From Scratch' should give you a basic understanding.

From your first post:..."i dont know what it means by the co-dinates"....the location of everything in the FS world, whether buildings or runways or flatten polygons, etc., is defined using one or more geographic coordinates. Each of the tools you will be using can obtain the required coordinate(s) from the location of your aircraft in FS.

To start your new airport:

First, properly install the tools including the required 'connection' modules for each (so they can read info from the sim).

Start FS and in 'window mode' slew to the approx. center of the area for your new airport. Make sure your aircraft is on the ground. It's best to find an area that is somewhat level as the type of flatten created by FlattEx (4 sided polygon) can yield some 'interesting' transitions to the surrounding terrain in hilly areas.

Make note of the coordinates and altitude** of your aircraft. This info is needed to fill in the 'Airport Properties' dialog for a new airport in Afcad. This should be the only time you'll need to manually enter the info as from here on, Afcad and the other tools can grab the info from the sim.

Minimize FS and start Afcad, select File>New Airport and away you go......  

Dave

** the ground elevation at your location is slightly below indicated aircraft altitude. In the default Cessna the difference is about 3.5 ft.