Trying to figure out how to enter an airway into my flightplan in FS NAV.  I'm sure I'm forgetting to do something fundamental. For instance, I am loading the flightplan for KSAN - KJFK and it begins like this...

KSAN BRDR5.IPL J18 SLN J24...

I know how to program the SID with the Imperial transition and the SLN VOR, however, how do I input the J18 and J24 airways? Trying to get the plan as accurate as possible.

Thanks.