Here is my best "Technicals for Dummies" explanation. BIG INSTITUTIONAL MONIES CONTROL THE DIRECTION OF THE MARKETS. When they buy the markets respond. Period! All of the day traders, investors, etc. combined buying a stock at the same time will not move higher of there is large institutional selling. If institutions are doing little or no buying or selling then markets move at a different pace.
NOW, with that understanding established, technical bottoms (support) form because institutions are buying all/any volume that is selling. It's just the opposite for tops (resistance) because the institutions are selling as much as people are willing to buy, and they are buying/selling more, in bulk, than the general market. This is why one of the most valuable tools a professional trader has is a market maker tracker that includes a "lot" volume monitor. I can see that GE average trade is 178 shares for today. I have a minute/5 minute volume tracker pulled up and it shows an average of 222 shares trading. Ok, that is slightly higher than the overall daily volume but it certainly isn't institutional action. When I see a minute chart crunching out multiple 10k-100k share lots THEN we have institutional buying in play. When it takes the 5 minute average to 25k+ avg lot then it means something.
Pro traders can see this for individual stocks and for the market as a whole. It's ONE EXAMPLE of the dozens of tools used.