There is a flat side(which are more comfortable) and the side with all the little spikes parts, what side is supposed to be up in the shoe?

Lol. Why would you buy these and wear the flat side? If you want pressure point stimulation get these. If you don’t—just like—wear your shoes regular... other wise, why

Where are these made?

Do not know where they're made but they certainly help sore feet. I use them in all my shoes. Just made a convert of my husband too. Definitely recommend for sore feet.

Is there a way to please as accurately as possible describe how firm/hard the nubs are?

The nubs are firm. If you’re a sensitive flower it might take time to acclimate to, but once you do the sense of relief the acupressure provides is unparalleled. I like to joke that I can’t stand up without these now. But yeah, if you never go barefoot and have the foot skin of an adult baby, I recommend trying your feet to these. Ten minutes to an hour at a time. You won’t regret it. Unless your feet are permanently baby feet. Then, idk