The Fed's discount window refers to the rate the Fed will lend money to its member banks and is arbitrarily set by the Fed. This is the "Fed funds" rate that is set periodically. This is the rate at which banks borrow to meet their reserve requirements (or more recently, because they'd like to speculate). It is important to note that when this money is borrowed, it is created out of thin air by the Fed.
Open market operations refers to the trading of bonds. The Fed owns bonds and they may enter into the bond market to buy and sell those securities. It is also important to note that if the Fed decides they'd like to buy bonds, this money is created out of thin air.