Dow theory is old theory about behaviour of stock price . It takes into account the major tops and bottoms of the chart ( the chrt considered as annual chart ) it also takes the volume into consideration and concludes that the higher top and higher bottom signifies bullish trend. Whereas low top and low bottom signifies bearish trend.
Support- This is simply a floor of prices, whether ascending, descending or level. It’s an area where prices tend to return to for varying periods of time.
Resistance- It’s a ceiling of prices, whether ascending, descending or level, and again, prices tend to return to common areas over varying periods of time.