An NCA file is a Nintendo Content Archive, which contains game data dumped from a Nintendo Switch game card. It stores multiple files that contain Nintendo content, such as firmware or a Switch game ROM encrypted with AES-XTS encryption. NCA files are similar to CIA files, which are used to store Nintendo 3DS content and WAD files, which are used to store Nintendo Wii content.
NCA files are typically extracted from .XCI files using Switch modding tools, such as HacToolGUI. After extracting the NCA file, you can use SciresM hactool to decrypt and extract files from an NCA file.