What's not to get? It's just the amount of money, measured in either BTC or in fiat, that has been traded in that trading pair, cryptocurrency or exchange in the last 24 hours.
What is the significance of volume
Volume is sometimes used as a
technical indicator which suggests the strength of a price move. If the volume is higher, it means that the price move is stronger as more money has the bearish or bullish sentiment of the market, while a lower volume suggests the opposite.
In future, try wording your question properly and don't use annoying colours.