Try to wrap your WebElement as shown below
Select dropdown = new Select(driver.findElement(By.id("identifier")));
After this select the required value in 3 ways. Consider an HTML file like this
<html>
<body>
<select id = "designation">
<option value = "MD">MD</option>
<option value = "prog"> Programmer </option>
<option value = "CEO"> CEO </option>
</option>
</select>
<body>
</html>
Now to identify dropdown use
Select dropdown = new Select(driver.findElement(By.id("designation")));
And to select its option say 'Programmer' you can do
dropdown.selectByVisibleText("Programmer ");
or
dropdown.selectByIndex(1);
or
dropdown.selectByValue("prog");