Warning: spoilers for do-we-even-have-to-say-it-at-this-point below.
By now, you've hopefully seen Avengers: Infinity War. Blah blah blah, a lot of people die, blah blah, not everyone, though, blah, Infinity Stones, blah. We're going to go ahead and skip all of the film's devastating and emotionally destructive events and focus on something much more proactive: how it's all going to get fixed. If you stayed for the postcredits scene, you'll know that Nick Fury (Samuel L. Jackson) has sent out a distress signal bearing a rather strange symbol. Turns out it's the insignia for a supercharged newcomer: Captain Marvel.
If you don't know, Captain Marvel is a hero who pops up in the '90s, but until now has not appeared in the Marvel cinematic universe. We're going to meet the hero in next year's Captain Marvel, which will drop shortly before the fourth Avengers film. But Captain Marvel isn't just a completely random person who bursts on the scene, and Nick Fury doesn't just call her out of the blue. Naturally, the two have a history that will be explored in the upcoming film.
Granted, Captain Marvel may stray from the the comic book origin story, but we have a feeling some of it will stay firmly in place. According to the official bio page for Carol Danvers, our young hero begins in the Air Force and eventually gets hired into the CIA because of her promising start. And what do you know, the first official picture of Captain Marvel shows star Brie Larson standing in an aeroplane while wearing a flight suit. According to the comics, Carol meets Colonel Nick Fury as soon as she transitions from the Air Force to the CIA, and the rest is history.
As for why Nick Fury decides to call his old friend after half the universe is vaporized? Basically, Captain Marvel's powers are key to destroying Thanos in the comics. To clarify, the most important power, Cosmic Awareness, belongs to the original Captain Marvel aka Mar-Vell. Luckily, this iteration of the character will also appear in Captain Marvel, meaning the film version will either bestow Carol Danvers with some of those great intergalactic abilities, or the duo will arrive on the scene to kick Thanos's ass together.
Either way, Nick Fury's phone call is basically the crux of the entire universe at this point. It establishes his relationship with Carol Danvers, which we will go back to the '90s and witness in Captain Marvel. It also opens the gate to Thanos's weak spot, and gives us hope that not all of our favourite heroes are gone for good.