Once you have installed WikipediaPlus, you can set up your WikipediaPlus preferences either through the Tools/Addons menu option or by clicking on the logo in the bottom right corner (the Add-on bar):
Main Article: Website Configuration
This pane allows you to change which sites Wikipedia+ checks to ask for suggestions.
This pane is for configuring the Wikipedia+ GUI.
This pane is for managing how Wikipedia+ behavior, such as when you click on a page suggestion. Should suggestion buttons open in a new tab or a window, in the foreground or the background etc.
The Pagenames tab lists PageNames which Wikipedia+ should not check for sites of interest. You will probably not need to change this. As well as literal PageNames, you can use a name ending with an asterisk to matches a set of pages (e.g. 'User:*' tells the extension not to bother searching for the Wikipedia users' pages).
Showing Wikipedia+ version number.
See the advanced configuration options for a couple more possibilities which may be of interest to some users. These have no GUI.