Hi Peri,
These buttons need to be created for you, and uploaded into the Design Studio to use in emails. You can also, in a program within Marketing Activities, choose New > Import Program > SOC Button Library (I have never used this, but if it's called Button Library, then it must have buttons, right?). Another option is to use a table and just change a few values, which adds flexibility.
If you want to use a table rather than an image, you can insert this HTML into the HTML email editor where you want the button to be, and change any values that you need to. (These values would be the link, button text, pixel width, and color. But also potentially table class, font, font size, padding, alignment...)
<table class="m-pb10" style="font-family: Arial, sans-serif; font-size: 20px; overflow: hidden;" cellspacing="0" cellpadding="0" width="200">
<tbody>
<tr>
<td style="padding-top: 13px; padding-bottom: 13px; background: #ee5315; text-align: center;"><a style="border: 0; color: #fff; text-decoration: none;" href="http://www.google.com">Click Button</a></td>
</tr>
</tbody>
</table>