it requires some planning.
Dave created index files in the directories and plugins to achieve this result on that site
for example, if you have a details page like:
items_detail.php?ItemID=1
and you wanted to use the product name "Widget A" to load it, you could create a new folder and index file:
/Widget_A/index.php
in that file add a plugin and use the plugin source:
../items_detail.php?ItemID=1
now the address
/Widget_A/
will actually load
/items_detail.php?ItemID=1