Last price, volume and what a candle is made of

The bid and ask tell you what could happen next. The last price and volume tell you what already did. Charts are built almost entirely from these two numbers, so it is worth knowing exactly what they mean and, more importantly, what they leave out.

Last price

The last price is simply the price of the most recent completed trade. Nothing more. It is not "the value" of the asset and it is not what you can trade at right now.

Three things beginners get wrong:

The last price can be stale. In a thin stock, the last trade might have been ten minutes ago. The bid and ask have moved since. The number on your screen is history.
The last price can be an odd lot or an off-exchange print. A single 5-share trade counts just as much as a 50,000-share block when updating "last".
Your fill will not be the last price. If the last trade was $50.01 and the ask is $50.03, a market buy fills at $50.03 or worse.

If last is above the ask or below the bid, something is off (usually a delayed feed). Free quote feeds are often delayed by 15 minutes; check whether yours says "real-time".

Volume

Volume is the number of shares (or contracts, or coins) that changed hands in a given period. One trade of 100 shares between a buyer and a seller adds 100 to volume, not 200. Volume is the closest thing you have to a measure of how much agreement is happening at a price.

What volume tells you:

How liquid the market is. A stock trading 50 million shares a day will absorb your 100-share order without noticing. One trading 20,000 shares a day may not.
How much conviction is behind a move. A 5% rally on three times normal volume means a lot of people agreed to transact at higher prices. The same rally on a tenth of normal volume means a few small orders pushed a thin market.
When something has changed. Volume spikes cluster around news, earnings, index rebalances and expirations.

What volume does not tell you: whether the buyers or the sellers were "in charge". Every share bought was also sold. "Buying volume" and "selling volume" as shown in some apps are estimates based on whether each trade happened nearer the bid or the ask, and they are noisy.

Relative volume

Raw volume is only meaningful compared to normal. Traders use relative volume (RVOL): today's volume divided by the average volume for the same time of day over recent sessions. An RVOL of 3 means three times the usual activity. Most scanners and charting tools show this, and it is far more useful than the raw number.

Situation	Volume	Likely interpretation
Stock up 6%, RVOL 0.4	Low	Thin move, easily reversed
Stock up 6%, RVOL 4.0	High	Something real happened; many participants involved
Stock flat, RVOL 5.0	High	Big buyer and big seller cancelling out; watch for a break
Stock down 6%, RVOL 0.3	Low	Possibly one motivated seller in a quiet market

What a candle actually is

A candlestick on a chart summarizes all the trades in a period, say five minutes, into four numbers:

Open: the price of the first trade in the period.
High: the highest trade price.
Low: the lowest trade price.
Close: the price of the last trade.

Plus the volume for that period drawn as a bar underneath. That is it. A candle knows nothing about the bid, the ask, how many orders were placed and cancelled, or who was trading. It is a summary of completed trades, and every pattern you will ever read about is a pattern in that summary.

This matters because a lot of what looks like "the market doing something" on a chart is just the summary artifact. A long wick on a one-minute candle in a thin stock might be one small market order hitting an empty book. On a daily candle of a liquid stock, the same wick represents millions of dollars of real disagreement.

Key idea: Last price is the most recent agreement, not the current one. Volume measures how much agreement happened. A candle is just a compressed list of agreements. None of them show you what buyers and sellers are willing to do next; only the order book does that.

A note on different markets

Stocks: volume is reported in shares and is consolidated across all exchanges in the US, so the number you see is the national total.
Futures: volume is in contracts and, because each contract expires, you look at the "front month" volume.
Forex: there is no consolidated volume, because the market is OTC. Your broker shows their tick volume. Treat it as a rough proxy at best.
Crypto: volume is per exchange and some venues have historically inflated it with wash trading. Cross-check between a couple of reputable venues.

Try it: Pull up a one-minute chart of any stock during market hours. Find the candle with the biggest volume bar in the last hour. Then find the one with the smallest. Look at the size of the two candles. Notice how often the tiny-volume candle has a range as big as or bigger than the high-volume one. That is the difference between a move made of agreement and a move made of absence.

Recap

The last price is the most recent completed trade; it can be stale and it is not your fill price.
Volume counts shares traded once (buyer and seller together), and matters only relative to normal.
Relative volume (RVOL) separates a real move from a thin one.
A candle is just open, high, low, close and volume; it shows completed trades, not intentions.
Forex and crypto volume figures are partial or per-venue; treat them with caution.