Xochitl Gomez makes her Marvel debut as America Chavez in "Multiverse of Madness," and while we might not know much her exact role in the MCU, we do have some significant background information on her character from the comics. America boasts superhuman strength, speed, and durability, as well as flight, but her signature power is the ability to open star-shaped portals that allow her to travel instantly across the multiverse, which makes sense considering the movie in which she's being introduced. She's been a member of various incarnations of the Avengers as well as other teams like the Ultimates.
America originally believed herself to have been born in an extradimensional paradise called the Utopian Parallel, which was responsible for giving her superpowers and which her mothers sacrificed themselves to save. Recently, however, this story was been called into question with the appearance of America's previously unknown sister, who told America that the Utopian Parallel was actually a private island research facility on Earth, and America's powers are actually the result of genetic experimentation (we're guessing "Multiverse of Madness" will go with the better-known version of the backstory, but you never know).
Regardless, America brings some much-needed LGBTQ+ representation to the MCU, as she is a lesbian and appears to be sporting a gay pride pin on her costume in the trailers, as well as the words "amor es amor" scribbled on her infamous American flag jean jacket.