System.Random generates pseudo-random numbers.

A different seed is picked, based on a time-like value, whenever the constructor is called without any arguments.

Random random = new Random();
Console.WriteLine(random.Next()); // int 0 to 1,844,349,103
Console.WriteLine(random.Next(6)); // int 0 to 5
Console.WriteLine(random.Next(1, 4)); // int 1, 2, or 3
Console.WriteLine(random.NextDouble()); // double 0 to just before 1