Puzzles anyone?

KP ZH OHIYKWR VOZQROF CXFJOFOJ Z WVXJOHV TDXYJ VROB SO WOHVOHQOJ VD JOZVR?
And here is your hint:
P=F

RXS ADYNT NFYVIE FR YCX SIWMN PXOYDWFRA O VZOR IP NCIXEOMXWN: "OSZ FR YCX POEFZT."
And here is your hint:
E=M

DJTM BKPMB PQYYMFD QBM QNDJYRXMYF AJBAMD.
And here is your hint:
R=U

RU M LNYFE YU EZRWYVYEZANV NRGA YD MHXNMO, GYAV XZMX HMOA RX M XNMRW YU XZYFLZX?
And here is your hint:
N=R