The plugin's documentation addresses that very topic under two headings:
Rewrite-Based vs (Sub-)-Domain-Based
As I don't know the first thing about htaccess or DNS, I chose fot both of my farms the rewrite based approach and let the plugin handle the necessary configuration setup.
I find in my .htaccess file (in the root folder where the dokuwiki farmer lives) the following lines:
# Options added for farm setup by farmer plugin:
RewriteEngine On
RewriteRule ^!([^/]+)/(.*) $2?animal=$1 [QSA,DPI]
RewriteRule ^!([^/]+)$ ?animal=$1 [QSA,DPI]
Options +FollowSymLinks
# end of farm configuration
This is the URL for one of my animals:
http://192.168.1.69/dokuwiki/!things/