After you receive the trees keep them in a shed or outdoors.
Do not leave the trees with the roots exposed for a long period of time.
Although they are dormant in winter if they dry out they might die.
Keep the roots covered (in a bag) and if you cannot plant in the next couple of days stick the roots into some damp compost or sand or even a small trench in the ground.
Planting
No need to dig a hole or enrich the ground. Trees are tough.
Just make a slit in the ground with a spade and widen it out a bit by rocking the spade back and forth. Get the roots into the slit.
You should be able to see the depth it was previously planted at and do the same depth again.
Press down with your foot to close the slit. If you plant into grass you might put down cardboard for about a meter around the tree and cover with bark or another mulch.
This keeps the grass down and gives the tree a head start.