Dow theory is the old but golden concept.
It is important technical analysis tool which shows the price Bullish trend and Bearish trend by which traders can take buy sell decisions. Minimum 2 years data required with daily charts. It does not gives the characteristics of the price trend.
High bottom and high top with high volume during break out the Low top is Bullish trend
Low top and low bottom with high volume when break out Previous High bottom is Bearish.
Support is the Buyers price zone which is comfortable price for buyers ready to buy. Resistance is sellers comfort price zone in which the Sellers happy to sell the stocks.