Using warm water - to make bread within around 4 hours, and when the weather and temperature of your kitchen are around 21 degrees Celcius, it's a good idea to use water that is around 34 degrees C. If you want to go for a longer fermentation (in the fridge overnight, for example) to get a better flavour and texture to your bread, use cooler water. Don't think for a minute that you can't use cold water, your dough will simply take several hours longer to rise. Beware though, above 40 degrees C and the water will kill the yeast.
Leaving the dough to rise in a warm place - This is not necessary. Before the days of central heating it was necessary to find somewhere warmer than completely freezing to let bread rise, so that it didn't take forever. Now that most houses are a fairly consistent temperature most of the year, it's best to let dough rise at room temperature. Dough that is allowed to rise at too warm a temperature will end up being a bit flat and crumbly.