At CineEurope yesterday, Disney promoted a number of upcoming Marvel Studios releases including Ant-Man and The Wasp, Captain Marvel, and Avengers 4. Since then, a number of false reports have started doing the rounds in regards to what was shown, including a scene revolving around Iron Man and Ant-Man discussing different realities and the Infinity Stones. Well, those claims are false!
In reality, Avengers 4 was simply referred to as "Avengers Untitled" and a clip was shown of Marvel Studios President Kevin Feige sitting in a chair and apologising to exhibitors for there being so few heroes left to sell to their customers. This was filmed specifically for those in attendance and the only tease for the sequel was that the remaining heroes are going to have to come back together as a team.
As for Captain Marvel, a few brief scenes from the movie were shown and that footage highlighted both her as a character and her powers. The gist of it was that Carol Danvers is the Marvel Cinematic Universe's most powerful hero and that she's set to become the new face and leader of this shared world moving forward. Needless to say, you shouldn't expect this featurette to be released online.