// Connect to the database
// ... 

var command = conn.CreateCommand();
command.CommandText = @"
  SELECT
    Language, Percentage
  FROM countrylanguage
  WHERE CountryCode = 'RUS'
  ORDER BY Percentage DESC";
var reader = command.ExecuteReader();

// Get the data
if (!reader.Read())
    return;

WriteLine(reader.GetString(0) + ": " +
    reader.GetFloat("Percentage"));

// Get all rows
while (reader.Read()) {
    WriteLine(reader.GetString(0) + ": " +
        reader.GetFloat("Percentage"));
}

// Close the connection
conn.Close();