The problem is that you’re calling List<T>.Reverse() which returns void.
You could either do:
List<string> names = "Tom,Scott,Bob".Split(',').ToList<string>();
names.Reverse();
or:
IList<string> names = "Tom,Scott,Bob".Split(',').Reverse().ToList<string>();
The latter is more expensive, as reversing an arbitrary IEnumerable<T> involves buffering all of the data and then yielding it all – whereas List<T> can do all the reversing “in-place”. (The difference here is that it’s calling the Enumerable.Reverse<T>() extension method, instead of the List<T>.Reverse() instance method.)
More efficient yet, you could use:
string[] namesArray = "Tom,Scott,Bob".Split(',');
List<string> namesList = new List<string>(namesArray.Length);
namesList.AddRange(namesArray);
namesList.Reverse();
This avoids creating any buffers of an inappropriate size – at the cost of taking four statements where one will do… As ever, weigh up readability against performance in the real use case.