Frame SQL query using String formatters

The string.Format method is a static method that receives a string that specifies where the following arguments should be inserted, and these are called substitutions.
In source code we need to use to frame the SQL Query
public bool SaveData(string firstName, string lastName)
    {
         String connectionString = ConfigurationManager.ConnectionStrings["TESTDB"].ConnectionString;
        bool result = false;
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
           SqlCommand cmd = new SqlCommand();
            cmd.Connection = connection;
             cmd.CommandText = String.Format("insert into Test_DB.dbo.PersonName(FirstName,LastName) values ('{0}','{1}')", firstName, lastName);
             cmd.CommandType = CommandType.Text;
            connection.Open();
            int count = cmd.ExecuteNonQuery();
            if (count > 0)
            {
                result = true;
            }
            else
            {
                result = false;
            }
        }
         return result;
    }

Like this we can frame the Update and Delete Statements also.  Please refer this link formore about the String Format function.