[anrakushi]

i can't remember the platform so don't shoot me for that.. but you want the kyoto/maibara line. take the trains going all the way to maibara (米原)
Maibara is still in Shiga Ken and takes 1hr 20 or so from Osaka. You can get rapid trains, they work on that ticket.

then from maibara you need to take the train to nagoya (名古屋) that takes about an hour with a rapid.

if you take locals by mistake i think i remember it being like about an extra 40mins on top of that. can't remember exactly.

you can't miss it, btw the whole trip one way costs ¥3260 so unless you are planing on doing more travel than Osaka - Nagoya and return, i wouldn't bother with the seishun 18.