some office supply stores sell a chart that can be used to figure out payroll deductions. you place a ruler on it and figure out how much to take out. you can look at circular E online at irs.gov.
you know that 7.65% will be withheld for FICA, maybe 1 or 1 1/2% for state disability
and the income tax will depend on your rate of pay and number of hours
it is possible that the gross will be so low as not reach the minimum at which any income tax is withheld
Go to IRS.GOV and download a free circular E; that has the withholding tables for all possible scenarios contained therein.
It's not a flat percent. It depends on how much you make.
To find out, plug all your numbers in at http://www.paycheckcity.com
It depends, based on the amount. The easiest way to figure it out is to look it up in IRS Publication 15 (found on their website). Your state has a similar publication available online.