Why would you claim yourself as an exemption in line 6a?

This information is only valid for filing taxes for the 2008 federal tax return

[due by April 15, 2009]

If you are single, and nobody claims you as a spouse [line 6b] or a dependent [line 6c] then you can check yourself [line 6a] to receive a tax exemption. This means that after you adjust your income after deductions, on line 42 you multiply the exemptions by $3,500, and these get removed from your income.

For example, if your adjusted gross income was $20,000, the exemption from line 6a [yourself] would be $3,500 removed from the $20,000 to make $16,500. This number would go in line 43 [Taxable Income]. So when you go to look yourself up in the Tax Table, you would not look up $20,000, but $16,500 as your taxable income.

The Tax Tables begin on page 258 of Publication 17 titled "Your Federal Income Tax". The cover is blue, with a bunch of pictures. They are in your local library, and post office. You can just read them step by step and fill out your own taxes. It is boring, and might require addition and subtraction skills, with occasional multiplication.