[Asterisk-Users] TDM400P specs clarification

[varun_saa at vsnl.net]

Hello,
      I need some clarification on TDM400P.

While browsing the Digium site I see that the TDM400P wildcard 
is being used as base card for other TDM series cards.

I wanted to know what basically the TDM400P card offers. 
If you see the specs it says :

" The Wildcard TDM400P is a half-length PCI 2.2 compliant card 
that supports from one to four telephone interfaces for connecting 
analog telephones or analog lines to a PC "

The term : 

" one to four telephone interfaces for connecting 
analog telephones or analog lines "

In terms of FXO and FXS what does it mean. I can see that
it has four RJ 11 sockets.

How will you decide which of the four interface to use for
what. I mean FXO or FXS.

Thanks in advance.

Varun