Gamepedias in Gamereactor are not like the well known wikis pages. We work more forum-like style where you can build threads and articles inside, as in picture:
It's really easy to create a new Gamepedia by using the "Create a New Wiki" button placed in gamepedia main page.
Already you have your new Gamepedia done. Now. it's time to fill it with Subjects and Articles.
To make a new Subject -or topic- you just need to go to your recently created Gamepedia, and select "New subject" from menu as in picture. There you can fill your subject title but also you can write your first article for that subject.
If you habe been following all steps, then you already have a Gamepedia with a subject and probably an article. But you want to write another article/entry for an specific subject, right?
To make a new article you must be sure you already are in the subject page you want to include your article. It's very important that you doublecheck you are in that page. If so, simply use the same procedure as writing subjects. Go to Menu and use the "New article" option.