You hold the foambaord in place with long #6 or #8 screws. Make sure
that you don't overdrive them, otherwise the points will come up through
he 5/8th" plywood sub-floor into your linoleum or flooring. You could
use adhesive, but then it isn't removable, and you have to find a way to
support the foamboard while the adhesive dries anyway.
Best of luck,
RJ