I've created one, but can't seem to find these options that are stated on the help page? Can anyone help me out? I'm sure the solution is very obvious and I'm just an unobservant doof.

You have to go into your Account Settings and set yourself to Advanced Editing or something similar. I had to figure that out myself recently as well. ^^

One sorta convoluted way:
>Pools tab
>View Pools
>Click on yours
>Click on index view
>In the search bar copy the tag present for your pool
>Whichever post you need to add to your pool, add it in the "Edit" tab of the post
>It won't show up in the tags, but should be part of your pool

Yours is: 'pool:1427'

Thanks both of you, got it figured out! :)