Market structure reduces a chart to a skeleton: a chain of swing-highs and swing-lows. Rising highs and rising lows describe an uptrend, falling highs and falling lows a downtrend, and overlapping swings a trading-range.
Working from structure keeps analysis simple and consistent across instruments and timeframes. It also produces clear invalidation: if you are long because structure is bullish, the trade is wrong when a swing low breaks, with no interpretation required.
Structure is timeframe-relative and that is where most confusion comes from. An hourly downtrend can be one pullback inside a daily uptrend. Always state which timeframe a structure claim refers to, and expect lower timeframes to contradict higher ones constantly.
Related: break-of-structure, change-of-character, swing-high, swing-low, multi-timeframe-analysis