Danny, as Stephen said it is there and it's not intuitive to use Once you've created the mask you need to invert it (to see it) and tell
PSP that you're wanting to edit it. Then it works pretty much the same as
PS.
Unfortunately, you can't add a layer mask to an adjustment layer.
There are ways to use the
PSP mask so that it acts like
PS's quick mask, but I've never gotten that to work satisfatorily.