Contracting scrolls are used to activate summoning - it's just a way to give you a pet in the world map.

The only way to get them atm is RNG in XGNW packs, i know of people who had opened 1 every 2 weeks since we have XGNW and still got none.

To activate a summon, you need the purple stones (mysterious stones?), which you can get in group shop and events.