This is another critical step. Before the chicks arrive, you must have a warm, cozy spot all ready for them. If you wait until you get them home from the post office to turn on the brooder lamp, they are going to get chilled. Until you open that box, they are all keeping each other warm with their own body heat packed into a tiny space. Once in the brooder, they won't have that anymore and it won't take long for them to get chilled - which leads to stress, which leads to pasting up. We don't want that.
So, make sure your brooder is set up, the bedding is scattered, the filled waterers and feeders are placed as you see here - around the edges of the heat lamp's influence, not too far away from the center but not right under it, either. And turn on that lamp, get your thermometer probe on the bedding underneath the lamp, and make sure you have a nice, toasty 95 degrees happening. Depending on the outdoor temperature, it may take a few hours for the brooder temperature to stabilize, so keep checking and adjusting the lamp height as needed. You'll tweak it again later, but you want to be in the ballpark of 95 degrees now.