Guide : help in knowing the working of the USRP when we provide a frequency to capture in the usrp_r

Hi guys ,
I am trying to know the way how usrp processes when i provide frequency
to
the usrp_rx_cfile.py. Please someone eleborate me where i am actually
providing my frequency.
Where my frequency parameter is actually been fixed in which part of the
usrp … example : Daughterboard , ADC etc.
Thanks.