A wikilink is a link to another article on wikipedia, such as [[Sausage]], [[Bob Geldoff]], [[WP:SPIDER]] or [[User:Izdezine/You R A Creator]]. If you type that code, it appears as: Sausage, Bob Geldoff, WP:SPIDER or User:Izdezine/You R A Creator.
An external link is a link to another website, such as [http://www.google.com Google], [http://www.nicecupofteaandasitdown.com tea], [http://www.badgerbadgerbadger.com Badger] - and that will appear like this: Google, tea, Badger.
You should not use any external links within the article. External links should only be used as either references (to allow the reader to verify the facts), or - in very limited cases - as external links.
