Copying from Wikipedia to this wiki is permissible because both use the same license. However, it is necessary to include the proper acknowledgment so that readers can refer to the original and discover its authors.
Whenever you do such copying from a page in the English-language ("en") version of Wikipedia, please add the following template near the bottom of the page: "Wikipedia|" (inside double curly braces, i.e. {{Wikipedia|}}). Then before the final brackets paste the name of the Wikipedia article. You need to add similar attribution for other languages of Wikipedia and for other GFDL projects.
Note that Wikia sites are not intended to duplicate substantial portions of Wikipedia. You may copy all or part of an article (and its links and templates) to start off a page on the subject, but you are expected to adapt it so as to reflect this particular wiki's slant on the subject.