The first link below is to the general instructions for Form 1040 for 2012. The second link is specifically to the tax table. Please note, however, that the tax table is only good if you have only regular wage income. If you have items such as self employment income (1099MISC) or capital gains, then the calculation for taxes paid can be quite different (which is why I included the first link to the general instructions).
https://www.irs.gov/pub/irs-prior/i1040gi--2012.pdf
https://www.irs.gov/pub/irs-prior/i1040tt--2012.pdf
