Seamless mode doesn't work in virtualbox

So I followed @wendell 's vitualbox tutorial and I cannot work out how to change to seamless, host button (right ctrl) and l is unavailable. Also, the screen res of my computer isn't available in the options. (1366x768)

Also doesn't work on my other computer, not sure what to do here...

It doesn't do anything when I insert guest additions CD image, which is odd.

If you insert the guest additions does it appear in the virtual drive in windows?

Aha! Yes, thank you very much. Am honestly a dunce at this shit.

Easy to miss the first time....