POSTing to an Apache Server

This is the double CR/LF. The client.println is one, and the "\r\n" is the other.

  client.println("Content-Length: 9\r\n");

This string is nine characters long:

  client.print("testone=1");

All after the double CR/LF is the content.

edit: I could have sent the double CR/LF like this if it makes it clearer for you

  client.print("Content-Length: 9\r\n\r\n");

CR/LF = "Carriage Return/Line Feed"