Quote from crgarcia:
Providing liquidity means that the Fed lends more money and makes borrowing easier, with less interests for troubled banks and financial institutions.
All other things being equal this is bullish (goes up) for the stock market.
Taking liquidity away means the Fed makes borrowing more difficult, with more interest, in an attempt to "cool down" an "overheated" economy. It is usually bearish (goes down) for stocks.