Mail-order plants arrive bare-root or in pots with some soil. The bare-root plants will typically have wet newspaper or other material wrapped around the roots to keep them damp. The most important thing you can do is keep the roots damp. Not waterlogged, just damp. Add more water as necessary and seal the roots in a plastic bag if they dry out too quickly.
If the plant doesn’t have any leaves yet, then you don’t need to give it any light. Keep the plant as cool as you can, but above freezing. The plants have been refrigerated in the upper 30s to low 40s for the winter, so another couple of weeks won’t hurt.
When the weather gets better, you will be able to plant them. Take off the wet newspaper and spread the roots out in the hole. Plant it so the stem or trunk is at the same level with the soil as it was when it was growing before it was harvested.
If the new plant already has leaves or starts to get them, then giving it light will be necessary. If you determine that you won’t be able to plant it for a couple of weeks, then you can plant it in a temporary pot. You don’t even have to worry about spreading out the roots; just wrap them in a pot, cover them with soil, and water them. Give it as much light as possible. If there isn’t enough, the leaves will be white or light green and the stem between the leaves will stretch and become weak.
When the weather allows you to plant it, you will need to harden it off first. When the temperature is above freezing, place it outdoors in bright light, but not in direct sunshine. Increase the amount of direct sun a little at a time over a week or two. After planting, it may need protection from freezing at night, if the temperature drops too low.
We want to store bulbs and other dormant plant parts in paper bags or containers with lots of holes for good air circulation to help prevent this problem.