Either sow them fresh in ordinary compost and leave them to their own devices, or store them dry over winter and sow them in spring or keep them for years and sow them whenever you find the packet. They grow.
The only thing you have to remember is that they hate being in plant pots so the sooner you get them into the garden the better they grow. Of course you could just leave the seeds to fall on the soil and dig up the million plants when you need some more.