What kind of buttons? If you mean the buttons for editing the articles you need to add those through MediaWiki and it would be helpful if you are the owner or an admin in the wiki you're adding them to.
If you mean you want to add an image with a link, which is basically the easiest way to make a button icon, with a link assigned to it; perhaps you want to take a look at this page. To do that you need to upload the image to the wiki first.
To upload images to Wikianswers, you need to go here.
- See also: Can I add images to an answer?