how to add a bar on top of a alphabet ?

[Metariya]

How can I have a bar (a small horizental line, like the one we use for
average) on top of a alphabet like "Y" ?

 

[Suzanne S. Barnhill]

See http://home.earthlink.net/~wordfaqs/Overbar.htm

 

[Tywardreath]

If you need to use these characters often then I would suggest installing the
Micrsoft Maori keyboard. Details can be found here
http://www.microsoft.com/nz/hardware/keyboard/maori/default.aspx