They will hold hundreds of seeds so collect twice as many seeds as plants you want to grow. I pop the seeds into an envelope and keep them in the dark and frost free. make sure they are dry or they will go mouldy.

You can either leave the flower head with seeds in it for the birds or you can remove the seeds and pop them in a feeder. I put mine in a feeder or the local squirrels have a feast :o)

I have been feeding the birds for weeks now with mine, I have also kept a handful for next years flowers, I cut the heads off and scrape the seed away.
I always pop a silica bag into the box with my seed packets as it helps with the drying process and stops them going mouldy...