[Gello]

The button itself looks ok. It should be a transparent button with a "Go!" text. Is it in a <Frames> section?

This isn't the only way but it's a common way:

<Ui>
  <Script file="MyMod.lua"/>
  <Frame name="MyModFrame" parent="UIParent" etc>
    <Size/>
    <Anchors/>
    <Layers/> <!-- fontstrings and textures -->
    <Frames/> <!-- buttons and controls that receive mouse events -->
    <Scripts/>
  </Frame>
</Ui>

If you do:

<Frame>
<Button/>
<Frames/>
</Frame>

Then it won't see the button.