I've been taught that the Present perfect tense is used when an action happened in the past and it is important now (or when it happened in the past and it is still ongoing).
Though, look at these examples:
Carla can't play basketball. She has broken her leg.
Carla can't play basketball. She broke her leg yesterday
The first example is the same as the second one, but the 2nd example is just using simple past tense. So, why grammar says that we have to use Present perfect tense when the action has an influence in the present since I can use simple past tense and it would have the same influence in the present! (Like, the first example and the second one have the same influence in the present, because Carla can't play basketball today in these 2 examples)
I've been searching for a while and always says that "it is something that influences the present". But, if I say "She broke her leg yesterday. That's why she can't play" it would have the same meaning. So, that's why I am "confusion".