If you've installed a full Slackware installation you should've
alredy Apache and MySql in your system.

Lets edit some files:
vim /etc/httpd/httpd.conf
at the line DirectoryIndex index.html change to index.php

index

at he line ServerAdmin insert your email address

admin

uncomment (remove #) the line Include /etc/httpd/mod_php.conf

php

then save and exit with :wq

Edit timezone: vim /etc/httpd/php.ini
uncomment the line and add a zone: date.timezone = Europe/Rome (choose yours)

save and exit

Now run Mysql as root:

mysql_install_db --user=mysql

/etc/rc.d/rc.mysqld start

then /usr/bin/mysql_secure_installation to set password and other settigs.

chmod 755 /etc/rc.d/rc.mysqld

resart with /etc/rc.d/rc.mysqld restart

restart Apache with apachectl restart

Download Joomla installation package and unzip all the content in a folder, now as root
copy in /srv/httpd/htdocs all the folders and files with cp -r * /srv/httpd/htdocs.

With you browser and go to http://localhost where you will find the Joomla
installation procedure, once finished it will promt you to delete the installation folder:

page
so as root type rm -r /srv/httpd/htdocs/installation, now you can click on site or administrator
to build your offline site.

bbackend

For further info read the official Slackware Apache docs at:
http://docs.slackware.com/howtos:network_services:setup_apache_php_mysql