Is chess a sport and if so how is it one?

I would say no. According to The Free Dictionary, the definition of sport is: "Physical activity that is governed by a set of rules or customs and often engaged in competitively." Chess is governed by a set of rules. Chess is competitive. But there is no physical activity involved in playing chess. Therefore, chess is not a sport. Same with darts and Poker. There is no physical activity with these games, therefore, they are not sports.

However, the IOC who governs the Olympics considers chess to be a sport.