Count each element in array and displays which number occurs how many times?

Try this:

int[] array = { 3, 6, 4, 3, 8, 1, 2, 5, 3, 8 };

var query = ( from item in array
              group item by item into items
              select new { Key = items.Key, Count = items.Count() } );

foreach ( var item in query )
  Console.WriteLine(item.Key + " => " + item.Count);

Console.ReadKey();

Result:

3 => 3
6 => 1
4 => 1
8 => 2
1 => 1
2 => 1
5 => 1