The 'two sessions' is where the two main political bodies in China meet to discuss and plan policies involving the economy, trade, military, environment etc. If it is the same as this year, then it should last for about a week.
Some key things to look out for will be any revised views on China's five-year plan and perhaps their take on relations with the US, considering all the argument on human rights and trade.
With the main focus being on 'common prosperity' now, it will be interesting to see how much more commitment China will be willing to put in to achieve that goal. And of course, be wary about any economic targets that may be set out.