Doubt in ni USRP PAM Tx.vi

Hi,

I am very new to Radio Transmission and USRP and I am trying to make a PAM Transmitter but for taking hints I am taking clue from this ni USRP example. But I am not able to understand few things.Please someone help.

1)I can understand that the pam block below is doing the PAM generation but where is the message signal being generated?

2)Also what is PN Sequence, alpha in filter parameters and why is the CDB cluster in a loop??

3)MOST IMP: DOES ANYONE HAVE AN EASIER EXAMPLE OF PAM OR QAM TO START WITH??

I am attaching the vi