It's important to note that the amount of money you accept for that paper need not be what's written on it. I.e., you could sell a bond saying you'll pay back $1000 + interest and get only $981 for it, say, or maybe $1017 dollars for it, or any other number.
If the bond sells for more than its nominal value, then the effective interest rate you pay to borrow will be lower than the nominal interest rate, and if the bond sells for less, then your effective interest rate will be higher than the nominal interest rate.
The face value of the bond is what you will receive at maturity. When the bond trades in the intermediate term, its price is determined by prevailing and expected interest rates.
If the bond sells for more than its nominal value, then the effective interest rate you pay to borrow will be lower than the nominal interest rate, and if the bond sells for less, then your effective interest rate will be higher than the nominal interest rate.