How to develop database application in Network(LAN)

I assume you aren't planning on writing teh dabase server from scratch - that would be a very silly start to teh project! :laugh:

Install SQL server on one of the PCs - the Express version is fine for starters - and then you just need some code to run at the client and a connection string:
Try:

using (SqlConnection con = new SqlConnection(strConnect))
    {
    con.Open();
    using (SqlCommand com = new SqlCommand("SELECT iD, description FROM myTable", con))
        {
        using (SqlDataReader reader = com.ExecuteReader())
            {
            while (reader.Read())
                {
                int id = (int) reader["iD"];
                string desc = (string) reader["description"];
                Console.WriteLine("ID: {0}\n    {1}", iD, desc);
                }
            }
        }
    }

To find the connection string, try setting up a connection in VS with the Server Explorer pane:
1) Open Server Explorer.
2) Right click "Data connections" and select "Add connection"
3) In the dialog that follows, select your DataSource, and database, specify the security info, and press the "Test connection" button.
4) When the connection works, press "OK"
5) Highlight your database in the Server Explorer pane, and look at the Properties pane. A working example of the connection string will be shown, which you can copy and paste into your app or config file.