There is already lots of information if you use the search facility..
Anyway, If you don't want to spend a lot because you don't know if you will stick at it then you can get away with one of these for about a year of learning anything up to 1/8th truggy in spray size. - I get on with it just fine but it will start to die after about a year of regular use.
http://www.ebay.co.uk/itm/Mini-Airbr...kAAOSwEetV8-WK
Pressure wise it depends on what you are trying to achieve, however there is no pressure that ruins paint. Naturally at first if you don't have airbrush control then spraying at a high pressure for fades etc can lead to it splattering all over the body if you are too close to the shell - Anywhere from 15psi to 60psi is the normal range. If you want to fade into a dagger stroke then 60 psi, if you are doing really intricate detail like lights and grills then lower it to about 20psi etc.