It might be worth reading a synopsis of the AC1 plot to understand what is happening with the modern day storyline at the start of 2, but I wouldn’t play it first. AC1 is a fun game in its own way but it has a lot of weird repetitiveness in the way missions need to be completed that was streamlined in later games. Personally I played AC: Black Flag first as It was the newest when I started playing, then went back and started the series in order with AC1 and it was pretty jarring.