How does Vodafone Freedom Packs work?

This is how I think it works:
You opt-in to the pack (How do you do that btw?)
Top Up £10
You get 300 free texts and however many minutes it was...
If you don't use the texts/minutes by the end of the month, they disappear, but you still have £10 credit on your phone.

Please correct me if I'm wrong

Thank You,
Juliette.x