Have everything ready tonight. The post office may call you very early. Be sure and plug in your heat lamps before you go to pick them up or even plug it in tonight.
When you get them into where it's warm by the brooder, take them out of the box individually and dip their beaks in the water. Then set them down in their feed. If you have those long feeders that have holes in the top for them to put their heads thru, it's best to remove the tops for a few days. Yes, they'll poop in the feed, but they need easy access to it.
Once they've all been introduced to their water and feed, sit back and take a deep breath.
After that just keep an eye on your thermometer and more important than that, watch your chicks. A cold chick is peeping alot and huddling under the heat lamp. A hot chick is getting as far away from the heat lamp as possible. You want them to be moving around, in and out of the light, checking out their new enviroment.
Good luck with them!