How do i report taxes if i am self-employed.?

I quit my job at washington mutual in december of 2007 and in january i started my own business. I have a website where i sell my products, i moved outside the country to set up my production warehouse. I now live in El Salvador. and sell my products directly to customers in the U.S, Canada and all europe. My questions is, how do i report taxes and how is it determined how much i pay?. Any advice will be very helpfu guys! thank you for reading my question.