The man page for /etc/exports page defines the format of that file by saying `the file format is similar to the SunOS exports file', which is not helpful if you don't have access to the SunOS documentation.
The man page for exports(5) is included in the nfs-utils package. It includes an example section near the bottom. I'm not sure what else can be added to make it better.
I think it is the "similar to SunOS" comment is misleading, since Linux /etc/exports syntax is somewhat different from SunOS /etc/exports pages. (BTW: SunOS man pages are available on the web.) Someone from the nfs-utils team is working on updated documentation, but it will be several release cycles before it makes its way into the nfs-utils package. I think your best bet is still to follow the example in the exports(5) man page.