Sign up for a web hosting service that supports flash media server. Use one of Adobe's official flash media server web hosting partners. Assign a name you will use for your client side program and for your server side program.
Open Flash Professional and click "New" in the "File" menu. Click "Action" from the "Window" menu to begin writing the client side program. Write the client side code in the Actions editor that appears. Use the "Import" commands in the code to include the necessary classes to enable client server communications. Follow the syntax required for client server the Responder, NetConnection, and NetStatusEvent commands. Declare any variables needed for the client and server connections. Code the necessary connect, call and close methods to connect and disconnect the server. Click "Save" from the File menu and assign a name to your client side program.
Select File from the Flash menu bar and Click the "New" option, and then click the ActionScript Communication File (asc) option to begin writing the server side program. Write the code for the server side program in the text editor that appears. Type the client function in the asc file and then write the commands or information you want back to the client inside the client function. Include the application module. Save this file.
Upload your server side program to the Flash Media Server hosting provider you use. Test the client side program and the server side program to see if the client side and server side programs successfully send and receive commands. Use two computers to check if the two-player (client-to-client) game functionality works.