The R7RS standard is essentially R5RS (directly supported by Guile), plus a module facility, plus an organization of bindings into a standard set of modules.
Happily, the syntax for R7RS modules was chosen to be compatible with R6RS, and so Guile’s documentation there applies. See R6RS Libraries, for more information on how to define R6RS libraries, and their integration with Guile modules. See Library Usage, also.