To add a new page to the wiki dictionary you will need to edit an existing page and add a link to the new page or term which you want to create.
All you have to do is come up with a meaningful title and in any existing text put it into square brackets like this [[My new topic]] which will result in My new topic[?]. This will create a link in your text with a questionmark which indicates that the topic does not exist yet. (Just for the record, there is another way which would be to simply capitalize all the words and string them together in one word like MyNewTopic. PhpWiki will automagically recognize that as a hyperlink also, but this way of linking is deprecated on this site, i.e. the preferred way in the Elias wiki here is the use of square brackets for linking.)
Then you can go ahead and click the questionmark at the end of your new hyperlink, and the Wiki will give you a window for making the new page.
If you wish to link ot external documents, you might be better off providing a URL to it than trying to add the text of the document here. Details about how to do this can be found in the TextEditReference.
This Wiki does formatting by use of simple characters but also supprt some basic HTML tags (see TextEditReference). Other <tags> will just render like text. But knowledge of HTML is not necessary, Wiki is meant to be as simple as possible to encourage use.