You've to export the application to a .ear file (or .war, I don't remember right now).
Then to pick it up you must entry by browser to the WAS console (
http://localhost:9090/admin), on the left side you've an options bar and therefore the instalation is an intuitive thing.
Of course when you finish installing you've to pick it up as if it was a server (you've to do it in the WAS console as well). For further information I recommend you WAS Infocenter that you can find it at IBM web page
Eric