A great deal of Perl/Tk documentation gets installed as part of the Tk extension building process. Hence, a great deal of documentation is probably residing on your computer already.
More documentation is "in the works": there are several books dealing with perl/Tk in progress, an ongoing magazine column and a growing FAQ (the document you are presently reading).
The additional material you may want to look at can be split into Perl/Tk, Perl, Tcl/Tk, and X documentation categories: Perl/Tk Specific Documentation The man pages
With up to date Tk build kits the various perl/Tk pod documents are converted to your systems' helpfile format and installed as part of the perl/Tk "make install" process. If you have a recent verion of perl/Tk try something like man 3 Tk::Tk if this does not work check with you system administrator for the proper MANPATH.
In your Tk build Directory there should be a doc/ sub-directory in which there are a number of .htm files (after you make install). These files were originally Tcl/Tk man pages (from the man* sub-directories), but the *.htm files have been converted to Perl syntax and rendered in Html format. You can use the Perl/Tk web browser to view them locally with a command like: tkweb index.html
or you may view them on the web itself by installing them in a web-server directory tree, or by pointing a browser at: http://w4.lns.cornell.edu/~pvhp/ptk/doc/ The newsgroup
The newsgroup name is comp.lang.perl.tk and this FAQ will be periodically posted to that group (as well as a few other newsgroups). The newsgroup and/or the ptk mailing list are the appropriate places to post questions - yes even simple ones! (Although answers may sometimes be long in coming ... :-( The nTk/pTk mailing list
The mailing list is an Excellent supplement and complement to the newsgroup comp.lang.perl.tk. All messages mailed to the list are forwarded to the newsgroup. (But not all messages posted to the newsgroup are forwarded to the list.) Some Perl/Tk eXPerts only have Access to e-mail.
The nTk/pTk Mailing List Archive is a very useful source of information too, and is accesible at either http://pubweb.bnl.gov/~ptk/
or via FTP at ftp://ftp.ccd.bnl.gov/pub/ptk/archives/