What happens between the client (your Android app) and the server is loosely coupled, meaning that they are not related whatsoever except for the protocol with which they communicate, which for a web service is HTTP.
Usually a client (either an app or a web browser) makes an HTTP request sending parameters (e.g. login, password) with POST or GET methods. The server takes these parameters and processes them according to its needs.
This may sound obvious, but you say that all the tutorials are using php script, so you seem confused: your problem on Android? or is your problem in the server?
The code you need in your Android app is EXACTLY THE SAME regardless of the server technology (asp, cgi, jsp, php...) and database (MySql, Oracle...), because the HTTP protocol is standard.
Here is an example I copied from here to make a simple HTTP request with two POST parameters.
public void postData() {
// Create a new HttpClient and Post Header
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://www.yoursite.com/script.php");
try {
// Add your data
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
nameValuePairs.add(new BasicNameValuePair("id", "12345"));
nameValuePairs.add(new BasicNameValuePair("stringdata", "AndDev is Cool!"));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
// Execute HTTP Post Request
HttpResponse response = httpclient.execute(httppost);
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
} catch (IOException e) {
// TODO Auto-generated catch block
}
}