There are docs bundled right into the JasperReports Server download. The docs are downloadable separately from the same page. It includes several things that you're looking for:
$ ls -1 ./jasperreports-server-cp-4.5.0-docs
JasperReports-Server-CP-Install-Guide.pdf
JasperReports-Server-CP-Source-Build-Guide.pdf
JasperReports-Server-CP-User-Guide.pdf
JasperReports-Server-Web-Services-Guide.pdf
Jaspersoft-OLAP-CP-User-Guide.pdf
Mondrian-3.0-Technical-Guide.pdf
I don't know why the Community Edition does not include an Admin Guide. You could download the commercial edition of JRS from the jaspersoft.com site. That includes an Admin Guide. There are lots of samples which you might consider tutorials on the .com site as well.