Well, you start them in a brooder box with a lamp (a 100 watt light bulb is usually enough, depending how enclosed the brooder box is, on how many and what size the box is and the external temperature of where the box is at) so one end is about 95 degrees, but they can get out of that heated area.  Then, you raise the lamp each week so the temp is reduced by 5 degrees each week till the box is just the same temperature as the rest of the room (or in my case basement) and they aren't acting all cold.  You will be able to tell after a bit believe it or not.

You should stick to chick starter till about 18 to 22 weeks depending on the breed (it's more accurate to track age in weeks instead of months) then switch to layer mash.  The calcium in layer mash causes serious kidney problems if you start feeding it too soon, before their egg production is actually ready to get going.  If it's a heavy breed that starts laying later, then wait till the 22 week mark, if it's one of the early laying breeds like Golden Comets or ISA Browns, then you can start around the 18 week time.

Oh and you can turn them out with the other hens when they are very nearly the same size as the older hens, but keep an eye on them when you do.