If you only read this website, no more information is collected than is typically collected in server logs by web sites in general.
If you contribute to the site then you are publishing every word you post publicly. If you write something, assume that it will be retained forever: this includes articles, user pages and talk pages.
As only registered users are allowed to edit this site, all changes can be traced to a given individual. When you edit any page on this site then you are publishing a document - this is a public act and you are identified publicly with that edit as its author. If you libel any person or organisation then it will be possible to identify that you were the author of this defamation - neither the site, its managers, administrators nor its agents are responsible for, or accept any liability for material posted by contributors.
NB: All contributions are accepted on the basis that they are released under the GNU Free Documentation License 1.2. Details of the GNU License can be accessed at any time via the link at the bottom of each page, or by clicking this link.
Deletion of content
Removing text from the site does not permanently delete it and indeed anyone can look at a previous version and see what was there. If an article is "deleted", any user with "administrator/sysops" access on the site can see what was deleted. Information can be permanently deleted by those people with access to the servers, but there is no guarantee this will happen except in response to legal action.