Namespaces are the way DokuWiki places its pages into hierarchy. You can think of namespaces as folders or categories (both meanings can be true).
Namespaces can be physical. For instance, if someone creates/links to a new page like this:
[[newnamespace:newentry]]
DokuWiki will create a folder called newnamespace on the server where VQP is hosted, and place the file containing the entry newentry in that folder (as DokuWiki stores wiki pages as plain text files).
In this wiki, all 'letter startpages' (e.g. The page listing all NeoQuenya words starting with 'A') have already been placed in the appropriate namespace called nq (i.e. the NeoQuenya top-level namespace). Thus, any NeoQuenya entries that are properly created from these 'letter startpages' will be placed under nq (both physically and hierarchically). The same is true for the 'letter startpages' in the NeoSindarin section (the ns namespace).
By putting the entries in namespaces we can also have pages with the same name in different namespaces (e.g. we could have an page/entry called estel under both the nq and ns namespaces without any problems).
You can read further about DokuWiki namespaces on the DokuWiki website.
Entries can be tagged using the Tag plugin of DokuWiki; this allows a better categorization of the dictionary entries; for instance, by properly tagging the entries into semantic categories, one can easily view all NQ words categorized as 'birds' by simply clicking on the birds tag, or by using special search pages.
The syntax of placing tags in a page looks like this:
{{tag>namespace:tag1 namespace:tag2 namespace:subnamespace:tag3}}
You can also click on the Tagging icon above the text input field (towards the right-hand side), which will put the basic code in the source for you.
Let's say you have created a NeoQuenya entry which is a neologism for a kind of flower, and you want to tag it. Typically you would want to put the word into at least two categories:
In our example this word would be tagged like this:
{{tag>nq:nouns nq:semantics:plants nq:semantics:flowers}}
This will put the word in the nouns, plants, and flowers categories within the nq (NeoQuenya) top-level namespace.