I was able to install the software, but there is no documentation about how to create NTRU+X25519 keys and enable it. I checked manpages, mailing list and tried google. How is this done?
It looks like its a key exchange algorithm, not a host key algorithm. So you don't make keys with it, you just tell your client and server to try using it when connecting. You can specify it with the KexAlgorithms config property, like for example ssh -o "KexAlgorithms=whatever". Use ssh -Q kex to see what options are available on your installation.