I heard some stock brokerage provide "live snaps"? what are these & how do they help in stock investing? tks?

In full realtime data you can see the stock price changing on your screen as the buy/sells happen.
"Snaps" provide the same information at one point in time (ie it is a 'snapshot' of the market situation at that time).

The alternative is delayed price data (eg price you see may be 20 mins delayed) and so having snaps/realtime data means you are trading with more info.

Source:
https://ibkr.info/article/2830