A stock’s price is determined by supply and demand. Bulls buy when the stock’s is prices are too low and bears sell when the price reaches its maximum. Bulls increase the prices by increasing the demand and bears decrease it by increasing the supply. The market reaches a balance when bulls and bears agree on a price.

When prices are increasing upward, there exists a point at which the bears become more aggressive the bulls begin to pull back – the market balances along the resistance line.
When prices are going downwards, the market balances along the support line. As prices starts to decline toward the support line, buyers become more inclined to buy and sellers start holding on to their stocks. The support line marks the point where demand takes precedence over supply and prices will not decrease below that support line. The reverse holds true for a resistance line.

Prices often break through support and resistance lines. A break through a resistance line shows that the buyers have won out over the sellers. The price of the stock is bid higher than the previous levels by the Bulls. Once the resistance line is broken, another will be created at a higher level. The reverse holds true for a support line.