Verify that Perl works by putting a test script (http://wakaba.c3.cx/sup/kareha.pl/1109033191/4) in a file, uploading it to a server, and visiting that URL on the server. If you have a problem, it's either because of a permissions problem (easy to solve, just ask), or Perl isn't installed or broken (give up).
Create a database. This is the most tricky part. When you're done you should have the DBMS's host, the DB user, the user's password, and the DB name. This is slightly different for everyone, so if you have a problem, ask.
To install wakaba:
Download and unzip wakaba on your local computer.
Using the stuff from 2. in prepare above, edit the config.pl. The things you'll need to change in config.pl are: ADMIN_PASS (password you use to login to the admin interface, e.g.: http://wakachan.org/os/wakaba.pl?task=admin), NUKE_PASS (similar to ADMIN_PASS, but used if you want to do something dangerous with wakaba), SECRET (just insert random gibberish), SQL_DBI_SOURCE (see 2.), SQL_USERNAME (see 2.), SQL_PASSWORD (see 2.).
Upload all of wakaba's files, including the changed config.pl, to your host.