The first case is a self-explicative one liner, it doesn't need an external function.

    var evenNumbers = Enumerable.Range(0, 40).Where(i => i%2 == 0).Select(i => i);

Private methods must group non-elementary steps. The second case is a perfect example that explains why it is so much better to use a private method because now you have a method that groups both sub-methods and you don't need to call always two different methods in a bunch of places. In this way you decreased code duplication increasing clarity.

    private void ProcessLogs()
    {
        var events = _logProvider.Read();
        events.Where(e => e.IsError).ForEach(SendErrorAlert);
        events.Where(e => e.IsWarning).ForEach(SendWarningAlert);
    }

And the method name seems quite self-explanatory to me.

If you need to separate one method in paragraphs, and add comments that explain what each paragraph does then that code is SCREAMING for a refactoring, deleting all the useless comments and extracting that mess in properly structured Classes/Methods.