how to buy a tkt using miles on the partner airline?

[nechamaY]

hi there,
appreciate any one's help, since I am very new in this:

1.how do I use US airways miles on American, or Delta miles on AirFrance?

2. when I try to get a tkt for example from JFK-PLS (Caribbeans) with US Airways miles, even though I find a decent deal, the taxes and processing fees are way too much. is that normal, or I dont know what I am doing
 
again thanks.