To start from the beginning.
1. System Preferences > sharing > web sharing
turn on web sharing
You will be notified of two URLs
your personal URL:
http://yourmachine/~yourname -- directory for this is/ Users/yourid/Sites
the machine's URL:
http://yourmachine -- directory for this should be /Library/WebServer/Documents
http://localhost
Download Dokuwiki from download.dokuwiki.org and install it in either of these directories. Open Terminal and navigate to the install directory, for instance:
cd /Library/WebServer/Documents
Using Finder, copy the tarball to either of these directories, then:
tar -xzf dokuwiki_file.tgz
chown -R _www <dokuwiki>
Open a browser and run
http://localhost/<dokuwiki>/install.php
<dokuwiki> is a place holder for your wiki's name