Watch any chart long enough and you'll see it: price approaches a level where something important happened before, and behaves differently there. It stalls, fights, reverses — or punches through and accelerates. These are support (below, where buying has shown up) and resistance (above, where selling has shown up), and they're the most intuitive idea in charting because the mechanism is human memory, not geometry.
Why levels exist
Think about who's alive at an old level. Traders who bought there and watched price fall are waiting to "get out even" — supply that appears on any return to the level. Traders who sold there and watched price rise regret it and want another chance — demand waiting below. Add the traders who simply observed that the level mattered once and pre-place orders around it, and the level becomes partly self-fulfilling: enough participants expecting a reaction there will collectively cause one. That's also the honest limit — a level is a concentration of intentions, and intentions change with every news cycle. Levels are zones of increased interest, not force fields.
Role reversal
The most useful single principle — a staple of Murphy's textbook treatment (paraphrase; see the breakdown) — is that broken resistance tends to become support, and broken support tends to become resistance. The mechanism is the same crowd, re-cast: once price breaks above a long-fought ceiling, the trapped sellers above are gone, the buyers who missed the move treat any return to the old ceiling as their second chance, and the breakout buyers defend their entry. You already met this idea from the other side in the breakouts course — a "breakout retest" is role reversal traded deliberately.
Drawing levels that mean something
Beginners draw too many lines; a chart with forty levels predicts nothing because it "predicts" everything. The working filters, from the Library's support & resistance page: prefer levels that have been touched multiple times; prefer levels where price reacted violently (big candles, high volume — the auction found real business there); prefer levels visible on higher timeframes, because more participants see them; and treat levels as zones a little thicker than a line, since nobody's memory is exact to the cent. Round numbers earn their keep too — humans anchor on 50s and 100s, so orders cluster there.
Connect the modules: a level is where to pay attention; candle shapes (Module 2) tell you what happened when price got there; structure (Module 3) tells you what the reaction means for the trend. A long lower wick, on heavy volume, at a triple-touched support, in an uptrend — that's four independent pieces of evidence agreeing, and evidence-stacking is the entire craft.
Assignment
On the same year-long daily chart you marked in Module 3, draw at most five horizontal levels — the five you'd defend in an argument. For each, note: how many touches, how violent the reactions, visible on the weekly too? Then watch that chart for a week and journal what happens at your levels. Most will do nothing (that's real data about levels), and one might put on a show.