i wish to develop an Android application which will go ahead and take content from online (server) and offer it within the application.

(ex. i go ahead and take the modern weather forecast, place the amounts in SQLite database or .txt file , place the database/txt file on the internet server then when i open the applying, the application connects&downloads the database through the internet and presents me with the modern forecast)

If you're able to references me with a example/video tutorial/book that are responsible for this problem i'll be very grateful!

What for you to do is creating a relaxation api that delivers data for the android application. E.g. you website has some content that you would like use within your application, then you may write a php script that simply returns that data inside a specific format.

E.g. mysite.internet/relaxation/fetchAllLocations.php?maybe_some_parameters

This could return locations in e.g. json format, here's a good example how that appears like:

[local zip code":33602,"shop_city":"Bielefeld","shop_street":"Arndtstrau00dfe","shop_snumber":3,"shop_title":"Mu00fcller","shop_desc":"Kaufhaus"]

Here's a good example for any relaxation api request:

http://shoqproject.supervisionbielefeld.de/public/gateway/gateway/get-shops-by-city/city/Bielefeld

So if you have your relaxation api setup you are able to cope with receiving that data together with your android phone. I personally use a static technique to get this data:

public class JsonGrabber{

public static JSONArray receiveData(){  
    String url = "your url";
    String result = "";

    DefaultHttpClient client = new DefaultHttpClient();
    HttpGet method = new HttpGet(url);
    HttpResponse res = null;

    try {
        res = client.execute(method);
    } catch (ClientProtocolException e1) {
        e1.printStackTrace();
    } catch (IOException e1) {
        e1.printStackTrace();
    }

    try{
        InputStream is = res.getEntity().getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"));
         StringBuilder sb = new StringBuilder();
         String line = null;
         while ((line = reader.readLine()) != null) {
                 sb.append(line + "\n");
         }
         is.close();
         result = sb.toString();
    }catch(Exception e){
         Log.e("log_tag", "Error converting result "+e.toString());
    }

    JSONArray jArray = null;

    try{
         jArray = new JSONArray(result);
    }catch(JSONException e){
            Log.e("log_tag", "Error parsing data "+e.toString());
    }

    return jArray;
}
}

Well thats all, after you have your computer data in json format you just need to parse it:

JSONArray test = (JSONArray) JsonGrabber.receiveData()

try { 
    for(int i=0;i<test.length();i++){
    JSONObject json_data = test.getJSONObject(i);
    int id = json_data.getInt("id");
    }
}

The net request should run in another thread, because it's really a time intensive process. So you have to cope with AsyncTask. Here are a few assets:

Painless Threading Multithreading for performance Hello Android Tutorial