What it means
Higher timeframes (HTF) move slower and carry more weight; lower timeframes (LTF) show detail for timing entries.
Example
One 1-hour candle contains twelve 5-minute candles.
In practice
The same market shows different pictures on different timeframes: an uptrend on the daily chart can contain a downtrend on the 15-minute chart. Traders choose a main timeframe that suits how long they hold trades, then look one step higher for direction and one step lower for timing.
Levels from higher timeframes matter more, because more traders see them and more money is positioned around them.
What to watch for
Dropping to a lower timeframe to find a reason to stay in a losing trade, or flicking between many timeframes until one agrees with you, are common ways of fooling yourself. Decide the timeframes before the trade.