COUPON RATE – The annual rate of interest payable on a security expressed as a percentage of the principal amount. The coupon rate, sometimes referred to as the “nominal interest rate,” does not take into account any discount (or premium) in the purchase price of the security.
CURRENT YIELD – The ratio of the annual dollar amount of interest paid on a security to the purchase price or market price of the security, stated as a percentage. For example, a $1,000 bond purchased at par with a 5% coupon pays $50 per year, or a current yield of 5%. The same bond, if purchased at a discount price of $800, would have a current yield of 6.25%. A $1,000 bond purchased at a premium price of $1,200 would have a current yield of 4.17%.
Here are some advanced concepts and formulas about them:
http://www.investopedia.com/university/advancedbond/advancedbond3.asp