how to connect database SQL Server with Visual Studio 2010?

app.config file with connection string like this

<configuration>
    <configsections>
    </configsections>
    <connectionstrings>
        <add name="ConnectionString">
            connectionString="Data Source=MyPC\MyDB;Initial Catalog=MyDB;Integrated Security=True"
            providerName="System.Data.SqlClient" />
    </add></connectionstrings>
</configuration>

Connecting to db

class DBConnection
    {
        #region Database connection method
        public SqlConnection Connect()
        {
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();
 
            try
            {
                conn.Open();
            }
            catch
            {
            }
            return conn;
        }
        #endregion
    }

Thanks

SP

For connectivity in visual studio
open Server Explorer
right click add Connection
Follow simple steps
After Creating Connection Right click on Database
Click on properties
In Proprties Connection String will be found.
Copy This String.

private void button1_Click(object sender, EventArgs e)
       {
           string cmd="select *from Admin where ID='"+txtFilenO.Text+"' and Password='"+textBox1.Text+"' ";
          SqlConnection con=new SqlConnection();
 
           con.connectionString="Paste Connection String";
            con.Open();
SqlCommand cmd1 = new SqlCommand(cmd,con);
 
           SqlDataReader dr = cmd1.ExecuteReader();
           if (dr.Read())
           {
               AdminMenu n = new AdminMenu();
               n.lblsser.Text = dr[0].ToString();
               n.Show();
               this.Dispose();
               this.Close();
               cmd1.Connection.Close();
 
           }
           else
           {
               cmd1.Connection.Close();
               MessageBox.Show("ID/Password is not valid");
           }
 
       }

it is connection from wizard,But You should learn meaning of each keyword, So see
Connection Strings

if you want to put Connectiion string in app.config

<appsettings>
    <add key="cnn" value="your connection string" />
  </appsettings>

and use as

string str = System.Configuration.ConfigurationSettings.AppSettings["cnn"].ToString();
           OleDbConnection con = new OleDbConnection(str);
           con.Open();