Snowdrops can be planted either in the autumn as dormant bulbs  make sure that they are freshly lifted and not hanging around in the garden unplanted; or as bulbs in growth which are moved in the spring just after flowering. They like rich, humusy soil.

They can take full sun or partial shade.

I found this on the net as well at About Landscaping.

You can plant snowdrops under deciduous trees without worrying that the snowdrops won't receive sufficient sunlight, since they bloom before the leaves come out on trees.

Additionally I plant daffodils in the woods, as they bloom b4 the leaves are on.

Sue

Yes, the leaves die down in summer.