Run configure, e.g.
./configure --prefix=/usr/local --sysconfdir=/etc --mandir=/usr/share/man
See configure --help for additional command line arguments.
Run 'make' and 'make install'. On BSD, you may need to use 'gmake'.
See INTRO.html, radvd.conf(8) and radvd.conf.example.
Setting up radvd is very simple, so the most frequently asked questions have been about what radvd doesn't do...
How do I set up the router running radvd to automatically configure an address from the prefix advertised in Route Advertisements from upstream?
-- You don't. By the specification, routers ignore RAs. You'll probably need to use manual configuration. But you can't use the same prefix on two links in any case unless you use something like proxy-ND (draft-ietf-ipv6-ndproxy-04.txt). You may need to re-think your topology; prefix delegation (e.g., manually or with RFC3633) may help.
How do I set up the router running radvd to automatically configure the interfaces to use an EUI64-based address?
-- You don't. The design philosophy of radvd is that it's not the router's configuration tool, but a route advertising daemon. You'll need to set up all the addresses, routes, etc. yourself. These tasks are something that system initscripts could possibly do instead.
I have a dynamic /48 prefix. How do I set up radvd to: a) set up interface addresses and routes on downstream interfaces, and b) advertise /64 prefixes from the /48 on downstream interfaces?
-- For a), this isn't supported. For b), radvd includes special support for 6to4 upstream interface but assumes that the interface addresses/routes are set up manually. This should probably be done in the initscripts or manually. (Though if someone were to send a patch for b), it might be incorporated.)
How do I set up radvd to do either unicast or multicast routing?
-- You don't. Radvd is not a routing or forwarding daemon. You need to set any appropriate routing/forwarding first, and then radvd to only advertise the prefixes to hosts as appropriate.