The foundation of most technical analysis tools is rooted in the concept of supply and demand.  There is nothing mysterious about support and resistance--it is classic supply and demand.  Remembering "Econ 101" class, supply/demand lines show what the supply and demand will be at a given price.

Resistance is equivalent to a "supply" line.  When prices increase, the quantity of sellers also increases as more investors are willing to sell at these higher prices.  When too much selling occurs, however, prices retreat.  When this happens repeatedly near a specific price level,  resistance forms at that price level.

Support is equivalent to a "demand" line.  When prices decrease, the quantity of buyers increases as more investors are willing to buy at lower prices.  When too much buying occurs, however, prices rise.  When this happens repeatedly near a specific price level, support forms at that price level.

Following the penetration of a support/resistance level, it is common for traders to question the new price levels.  For example, after a breakout above a resistance level, buyers and sellers may both question the validity of the new price and may decide to sell.  This creates a phenomena referred to as "traders' remorse" where prices return to a support/resistance level following a price breakout.

The price action following this remorseful period is crucial.  One of two things can happen.  Either the consensus of expectations will be that the new price is not warranted and  prices will move back to their previous level; or investors will accept the new price and prices will continue to move in the direction of the penetration.

When a resistance level is successfully penetrated, that level becomes a support level.  Similarly, when a support level is successfully penetrated, that level becomes a resistance level.
Use the Trendline tool to draw support and resistance lines on you MetaStock for Java charts.