You probably want to go and read the docs on the Realm project website.
You probably want to go and read the API reference on the Realm project website. The API reference is generated from comments in the source code of this repository.
You can generate the API docs locally by running sh build.sh docs from the root of this repository. This requires installation of appledoc. You will find the output docs/output/.
You can view the docset locally with tools like Dash or in Xcode directly with e.g. Docs for XCode using the packages generated in docs/output/ or via the links in the upper right corner of our online docs.