C#: How do you work with parallel programming?

1Parallel.For(0, 1000, i =>
2{
3    ProcessItem(i);
4});

1Parallel.ForEach(items, item =>
2{
3    ProcessItem(item);
4});

1var results = numbers
2    .AsParallel()
3    .Where(x => IsPrime(x))
4    .ToList();