When you've successfully downloaded the Perl source code, extract it from its archive. There are two steps required to extract the Perl archive; decompressing it using gzip, and expanding the archive using tar. To unzip the file, use the following command:
gzip -d latest.tar.gz
Then, untar the file using this command:
tar xvf latest.tar
As the tar program runs, a list of all the files being extracted from the archive will be printed on the screen. Don't worry about the output. A directory named perl5.6.1 or something similar will be created with all the Perl files inside.
Detailed installation instructions can be found in the README and INSTALL files; I'll summarize the process in the following sections.