Be sure to check out the official faq (see the usage section) to get up to speed with basic tasks.
After logging in, under the sidebar you should see an 'edit' link (as shown in the picture below):
You can then add the links to pages you want displayed in the sidebar manually.
If you see a wiki page that contains elements you want to reuse, you can see the page's sourcecode (in wiki syntax) by clicking the Show Pagesource navigation item.
In case you accidentally deleted a page, you can get the source for it back by clicking the Recent Changes navigation item and then diffing the revision you want to see with the current one (which will be blank in the case the page was deleted).
To remove a page, simply delete its contents and save it - dokuwiki erases it. If you delete all pages under a namespace, it will be deleted and will not appear in the index.
To upload any file to the wiki (zip archives, images, source files etc.) you need to be editing a page. You need to click the Add images and other files
menu item.
After uploading the file to a certain namespace, you can reference it with the image syntax, even if it is not an image. For example Form generator assignment.
Trying to redo the steps I took one year ago, I came across the following problems.
The creole plugin is no longer available at the address in the install script. The version available on the wiki project's site is for the newer version.
Same thing for the the include plugin, the original location is no longer available and I could not find other versions.
There is no way to upgrade - “Error: this script must be run as root”. If you try and do it manually you will break the wiki, so beware. Since the plugins are not to be found, upgrading the script or the docs to work with newer version is advisable.