The NFP/Nonfarm payrolls is a number of new jobs that is released by the US bureau of labor statistics. The number relates to how many individuals were employed in the previous month. In this case, December 2019 would be the period considered.
The nonfarm payrolls is as it says, it does not include any figures from the agricultural categories (farming etc).
The changes in the figures are what create the increased volatility as it tells investors how well the economy is doing and if it is growing. If there is a large gap between the actual number and the forecast then the market usually responds with strong moves as traders enter the market with their opinion based on the nfp statistics.
When the actual numbers are better than the forecast it is seen as good for the dollar (good performance, high job creation). When the actual numbers are worse than the forecast it is considered as bad for the dollar (poor performance, low job creation). In either of these cases the market usually responds accordingly however it does not always happen and if the difference between the actual and expected numbers is small, the market usually remains in the same state.
The news can be very unpredictable. Statistics that are positive for the dollar has in the past seen the dollar weaken in any event, obviously because there are other factors that also affect the dollar and the rest of the market so there is a lot to consider.
So what's the big deal?
Many traders anticipate massively on the day of NFP in the hope of making quick profits by taking advantage of the big moves that happen in a short space of time. The risk during this period is exponentially higher and the reality is that the volatility is a double edged blade. You can make a quick buck but your account is also at risk because of the increased volatility in the market.
I personally prefer to work with technical analysis where I can use key levels and signals from the market to substantiate my idea. I do not open any trades during high impact news events, I analyze after the close of each candle where I have definitive information to consider.
Every move has a signal, finding it is the art.