Suppose you got a List of Strings (any other will work, too) and you want to pick a random element from it. The first thing you do is initialize a new Random object. The you can use the Next() method of the Random object, passing the number of objects in the List as the upper bound:

List<String> AllStrings = new List<String>();
// add elements to List here
Random rndObj = new Random();
String RndString = AllStrings.ElementAt(rndObj.Next(RandomStrings.Count));