An uptrend is a series of higher highs and higher lows. A downtrend is a series of lower highs and lower lows. A downtrend line is drawn from the initial high to next highest high of the downtrend. Now, let's define support and resistance. Support is an area of prior purchases which acts as a source of demand for the stock on the way down.
Resistance is an overhead source of supply of stock to sell triggered by an area of prior purchases.
Unsophisticated investors will not sell their losers, they will wait until the price returns to their entry level so that they can end the pain by selling at a breakeven. Likewise unsophisticated investors who at a lower level and saw the stock run up significantly only to return to their purchase are likely to buy at their prior entry level. It is important to not buy in the face of immediate overhead supply or resistance, or short a stock with support or demand directly below your entry point. Trading positions should have some room to run. Typical patterns consist of breakdowns, breakouts, countertrend retracements in either bull or bear markets, pullbacks, corrections, and trend reversals.