C#.net How to create shuffle method for array

i need something like a void that will randomly set the index value to new index Random method or Shuffle please im new and i need help it's for school i tried to do this but it have a lot of errors

    int [] array = new int [10000];
    for(int arrayrandom=1;arrayrandom<=10000;arrayrandom++)
{
Random randomnumber;
    int takerandomnumer=randomnumber.Next(1,10000000000);
     array[arrayrandom]=takerandomnumber
}