Support & Resistance
Support
It is the price level where the demand for particular stock is very high, and buyers just BUY as it reaches that level, of course with stoploss few points below that level.
Resistance
On the contrary it is that price level where supply of a particular stock is very high and no trader/investor is willing to carry on with their long position and simply sell.
Note – Investors make money only by buying stock i.e when price moves UP, where as Traders make money both side by short selling a stock and again buying back at a lower level to make profit.
Here are some pictures which will help you determine support and resistance levels.
Also keep in mind that when a stock crosses its resistance, the resistance become its Support and similary when the prices fall below Support level, the support not acts as resistance.