yep, you need to read more about what you want to offer and how to set things up.
Zero is right, setting up a company is expensive in Chile, and takes a while to do.
People can register to issue boletas. They are (I think) classed as "2nd category" and are for professional services. So, people like Doctors, Kinesiologists, Dentists etc will often issue boletas (although they can also form companies and issue facturas). I am a web designer and I issue Boletas.
This page has lots of links to the diferent types of companies and individual workers. You might want to read Profesionales y trabajadores independientes.
http://www.sii.cl/contribuyentes/contribuyentes.htmAs for being able to write off your purchases, for the independent worker, you can do the same, up to 30% of what you earn, ith an upper limit.
When I looked into it I decided not to set up a company as it seemed too expensive and too hard -you have to involve lawyers and $$ here in Chile.