Opinions of the United States Supreme Court
Opinion texts are stored in Precedent format, a lightweight markup language that is easily translated to JSON, YAML, or your preferred structured interchange format. Case metadata is stored in YAML format.
Both formats are readable by programmers and non-geeks alike. Even if you've never looked at source code or computer data files before, you should have no trouble figuring them out.
Unless you are interested in contributing large changes or additions to the dataset, you should probably download a ZIP archive of the most recent versions of all files and work with those.
Those interested in contributing should note that the repository includes many files in many nested directories. Git is not optimized for such uses. The working tree takes up a lot of space and may make Git far less responsive than usual, especially on machines with slow mechanical disk drives. On the other hand, the repetitiveness of the plain text facilitates effective compression for local repository storage and network transfers. If any of this poses problems, feel free to use GitHub's web-based editor.