How do I use this building?

After you've built it, visit it via Manor -> Buildings and enter the name of an item you want to find more of (such as Vermillion, Rainbow Jar, Granite etc).

Then while exploring islands, there's a higher chance of that item appearing. The super rare ones (like Rainbow Jars) are still rare, as you can only find them in treasure chests, beast temples and magic shops. Materials like Vermillion will be visibly scattered all over the island to be picked up, though.

Thank you so much!