Yup that's about it - you need to tick the box on your card to say you'd like to attended the showdown if you qualify.
The are 9 places allocated at each GP and 10 at the last one.
Places are allocated based on your score and once you've qualified you can't qualify again.
When there are tied scores places are allocated based on countback - I.e. Starting from target 1 on your card, the first person to miss a target loses the countback.
If you don't qualify initially at a GP there's still a chance you could qualify at the GP at a later date, should one of the shooters decided they can't make it to the showdown.
It's worth checking the qualifier list after each event to see it there's been a cancellation which makes you're next in line to be allocated a place. (assuming you ticked the box)