Gen hook LM SAVANAAH

ALready have the gen prep and want to hook up our eu 3000 IS to it.It has a junction box in the front compartment that you attach your gen then it goes to a transfer switch.SO attaching the hot do i need too legs of 120 or will one work? I could jump from one hot leg to the other so would have 2 hot 120?I understand there is a yellow stopper that has to be removed from the transfer switch prior to activation.
THANKS AL