When you mark the checkbox in the Foris GUI, DNS tab, it should just work and make mymachine.lan names accessible (from DHCP). You can also change the suffix in there. /etc/hosts is not served over DNS by default but it’s easy to set up; see the wiki entry.
Note: some DHCP names might get filtered “unexpectedly” at this moment, for example those containing an underscore. That’s discussed in Log explanation