JSRs are formal documents that specify APIs in the Java platform.
It may take a long time before any of the APis become a standard part of that platform, so in the meantime you should be able to include JARs in your project that implement specific JSRs or APIs.
e.g. JSR 356 is a proposed standard for WebSockets.
JSR 250 introduces some helpful annotations found in the "javax.annotations" package.