What is volume and what it tells you about a move
Volume measures how many trades (or how much money) were traded in a period. It's the "fuel" behind price: a move with volume has conviction; one without volume is suspicious. Learning to read it adds a layer of information price alone doesn't give.
What it measures exactly
Each volume bar (below the chart) tells you how much activity there was in that candle: how many units changed hands. High volume means lots of participation and interest; low volume, little. It doesn't indicate direction by itself, but the strength or conviction behind the price move.
Volume confirms the move
The basic rule: a strong price move ACCOMPANIED by high volume is reliable, because there's real participation behind it. A powerful rise on low volume is suspicious: few are buying, so it may lack continuity. Volume tells you whether the move has "muscle" or is pure smoke.
Breakouts: the volume filter
Here volume shines. When price breaks an important level, the key question is: on what volume? A break on high volume is far more likely to be real; a break on low volume is often a false breakout (fakeout). Many traders won't trade a break if volume doesn't accompany it.
Volume divergences
If price keeps rising but volume decreases candle by candle, it's a warning: the rise is losing strength, fewer buyers are pushing. It's not a sell order, but a hint the trend may be exhausting under the surface.
Each market's nuance
Careful: in stocks and futures volume is real and centralised, very reliable. In spot Forex there's no centralised volume (it's a decentralised market), so your broker only sees ITS volume: use it as an approximation, not absolute truth. In gold via futures and in crypto it is fairly representative.
Where to start
Start using volume for one thing only: filtering breakouts. Before trading a level break, check whether volume accompanies it. With that filter alone you'll avoid a good chunk of the false breakouts that trap the impatient.