The heat lamp will be 18 to 20 inches above the birds in a cold environment and 24 to 27 inches above the birds in a warmer environment. When the heat lamp is too close to the birds, it causes excessive heat, so that they fly away from the area and cool down.
1. Heat Lamp -- most sources say to use this. A disadvantage is needing a piece of equipment (the heat lamp) with no other use, and possible fire hazard.
2. Heating pad inside a small homemade enclosure, or under a comercial heating block. The chicks only get heat when under the heater. Food and water are away from it, but they do okay. This partially simulates the way chicks are reared by a hen. As they mature they gradually wean themselves away from the heater and spend less time under it. There was a long thread on this in this forum. My post on it is here.
3. Under a boody hen. You induce boodiness by puting fake eggs (or golf balls) in a nesting box and see which hen wants to try to incubate them. Then you (ideally) move the hen to a small enclosure away from the rest of the flock, with a "broody box" smomewhat larger than a nesting box. A cardboard box in the neighborhood of maybe 18 inches in each dimension can make a good broody box. Just cut a hole in the smaller side for the hen to enter, with a lip of a few inches to hold bedding, and put in some fake eggs. After a few days, take away the fake eggs and introduce the baby chicks, watching to see whether the hen accepts them. This is now my prefered method.
Note: I actually usually keep the chicks in a small cardboad brooder under a heating pad for the first day, to make sure they have had plenty to eat and drink and are othewise okay, then give them to the broody hen maybe an hour or two before dawn.