It's essential you follow all the manufacturer's instructions on installing your chimenea or fire pit, these should include positioning it well away from anything in the garden that is flammable or likely to be adversely affected by the heat that is going to be generated. Both also need to be on a level surface in the open air and secure from falling over.
Only a few materials are required to light the fire: dry newspaper, kindling, well seasoned logs and a butane gas lighter or long matches. Fire lighters generally come in handy but are not essential if you have the correct amount of good dry kindling.
Well seasoned or kiln dried ash and oak which have a low moisture content are generally reckoned to be the best logs to use on any fire due to their slow burning and high heat output qualities. Any timber that you use must be as dry as possible as wet wood produces a lot of smoke but little heat, the opposite to what is demanded.
Logs can be obtained by the pallet load from many sources. Heat logs or briquettes are an alternative, these are made from compressed sawdust, widely available and, if good quality, will produce heat similar to seasoned logs.
Scrunch the newspaper into balls, some people prefer particular publications but this shouldn't really matter, and put these in the fire pit or chimenea. Next, place the kindling (with fire lighters underneath if used) on top of the paper in a grill pattern ie with two or three layers of kindling at right angles to each other. Finally, put a well seasoned log or two on top.
Lighting the fire isn't rocket science but can sometimes take patience and don't make the rookie mistake of leaving the lid on your chimenea chimney! You need the flue to expel smoke and create a good draft of air which sucks fresh air into the fire so the burn is as clean as possible.
Light the newspaper with the butane lighter or match, this will soon set the kindling (and firelighters) alight and then the logs placed on top will start to burn. When the kindling is exhausted, continue to place logs on the fire.
The eventual aim is not to encourage a raging inferno but to build up a mass of glowing embers, lots of flames may be an impressive crowd pleaser but it is the resulting embers that create the required heat that should last long into the evening.