I believe most loans are deferred through residency. And they don't take money from your paycheck - you have to make the payment yourself either through auto payment from your bank account each month or write a check.
As for how much it'll cost you, there are several calculators on the web to assist you with this calculation. It will depend on the interest rate of the loan and the amortization term (how long the repayment term is, whether 5, 10, 15, or even 20 years to pay the loan back).