From what you said, I figure wd1 is a second disk that you just added.
NetBSD is on wd0, and now you want to set up some space in wd1 as
swap. wd0 does not have any partitions etc on it.

If that's the case, first you'd need to make a partition in it. Use
fdisk(8) for that. Typically, something like "fdisk -u wd1" and then
making a partition is what you'd have to do. You can make that the
first partition maybe, give it a type of NetBSD (sysid 169) and
allocate some space in that. Maybe u can give the whole disk over to
NetBSD -- make one big partition of type NetBSD. Or maybe you can make
a partition with size equal to how much you want to allocate for swap.

fdisk(8) just makes a partition. After that, you gotta use
disklabel(8). Typically something like "disklabel -e wd1" and then
you'd follow instructions like Olaf said.

I hope this helps. I didnt go into too much details coz I wasn't sure
what the exact situation is. If you need more info, feel free to ask.

Thanks,
Rakhesh