Here's the part of the Tag application documentation that will be removed:
Tagging a page in structured mode
To access this feature, it is first necessary to define the set of tags to be used on the wiki. To do so, you need to go to the http://<server>/xwiki/bin/view/XWiki/TagClass page, edit it in class edition mode and enter the tags you want to use in the "Values" field. You can separate the tags using the "|" symbol (recommended), but also with a space or a ",".
Once this is done, you can choose between 2 ways of displaying those tags on a page in edit mode.
To setup the Checkbox display, you need to select "checkbox" on the TagClass page. Once this is done, users will be able to assign a tag to a given page by ticking the relevant box.
If you would rather use the Select display, you need to choose "select" on the TagClass page. This way, users can select tags by clicking on them, selected tags for a page being shown highlighted in blue.