My preferred approach is to use WindowWidth and WindowWidth to arrange objects:
Set the text object's horizontal alignment to center in the properties panel and then in the event sheet, if you want the text object to be on the bottom center of the window:
On start of layout, set text object's position to:
x: (WindowWidth - self.Width)/2
y: WindowHeight - self.Height
This works for any object, not just text. If you wanted the object right in the middle of the screen both vertically and horizontally,
x: (WindowWidth - self.Width)/2
y: (WindowHeight - self.Height)/2
For the buttons, check out part 2 of my tutorial on Creating a Memory Match Game. It shows how you can arrange a layout of cards that resizes and rearranges if the window size changes, but the technique would work just as well for buttons.
EDIT: You can read about the Anchor behavior in the manual, but I don't think it works well for centering.