In 1812 due to the war the USA initiated an income tax. The tax was stopped in 1817 after the war debt was cleared up.

The USA started it up again in 1862 with the establishment of the office of the Commissioner of Internal Revenue.

The civil war was the motivator for this tax and it was never repealed since.

Income Tax became permanent in 1913 with the 16th amendment.

Most countries have a scale whereas people who earn more pay more.

You can also learn a lot about income tax from the tax forms and instructions and the websites linked below..

Let me refer you to this site for 1040 forms of all kinds and the instructions that go with.
www.1040-forms.com

If you are self employed a payer or employer for your contracted services will want you to submit a W9 Form.

The income tax rates for 2011
www.taxman123.com/2011_federal_income_tax_rates.html

The income tax rates for 2012
www.taxman123.com/2012_federal_income_tax_rates.html

Are you interested in getting your tax refund...?
I bet you are. www.rc123.com/irs_tax_refund.html

Income tax humor - can there be any?
www.taxman123.com/tax_humor.html

Every year you should submit a W4 form to your employer so that the employer can be sure to deduct the proper amount of $$$ from your wages.
Here is some pertinent info: www.w4form.biz

Online Tax help. there are some warnings here so that you avoid a pitfall or two. www.rc123.com/tax_help.html