There are various types of brooder - the most common is a lamp on a chain, with either a special red coloured bulb or a 'dull emitter' ceramic bulb in it. You hang the lamp up, so the bulb is a foot or 18 inches above the floor and you allow the chicks space to get away from the heat if they want to. Often this is done by making a circle of corrugated cardboard 3 or 4 feet across, with the lamp at the centre. You can also hang your lamp over one corner of a large cardboard box or get special 'brooder pens' to keep the chicks in. You can also get a system called an 'electric hen' which is a heat-pad for chicks to sit under when they are cold. Someone I know broods her chicks very successfully in a cardboard box by her aga.
For more information about setting up a low-cost brooder for a dozen or so chicks, have a look at designs for two simple brooders.
Gradually, over a few weeks, as the chicks develop grown-up feathers, you raise the lamp a few inches at a time and eventually start turning it off during the day. It's very difficult to give a rule of thumb for this, as it depends on the weather and the temperature of the building your chicks are in. For example, in a hot summer, you might be able to start putting two week old chicks outside in a pen on grass for an hour or so every day. But in February, you wouldn't. As a guide though, even in the coldest weather, I would expect to have finished with the lamp completely by six weeks and in warm weather perhaps by four weeks.
To start with it is very important for the chicks to have a non-slip surface under their feet. They can be subject to something called 'splayed leg', which is made worse if they can't grip properly. Put them on corrugated card (rather than newspaper) from hatching to three or four days old, or a deep layer of woodshavings.
After two or three weeks, as they get bigger, some people keep them in a greenhouse - or put them out in to a greehouse in daytime. This tends to work well in spring or autumn - if it's very warm weather the greenhouse will be too hot for them. Also, however small they are, chickens are incompatible with growing plants!
The advantage of having them on corrugated card to start with is that if you put chick crumbs down on the card too, when they peck at them it makes a noise - this seems to encourage them to get the hang of feeding. Alternatively you can scatter the chick crumbs in an old carboard egg box or something similar for a day or two - anything that makes a noise when they peck it.
To start with you should provide them with a shallow dish of water, that they can't knock over or drown in. A deepish saucer with some pebbles in it will work; or there are special 'chick drinkers' that you can buy.
After six weeks you should move them on to 'growers pellets' rather than chick crumbs.