Let's begin by downloading the current version of Joomla.
Point your browser to www.joomla.org. On the home page, click on the Download button.
You'll be taken to the download page. Select the latest release. Make sure that you download the full package (the other versions are upgrades for existing Joomla installations).
The default download file is a ZIP file. Download this file to your hard drive.
Unpack the compressed file to a folder on your hard drive. If you don't have a software program to unpack files, check out http://www.7-zip.org for an open source file extraction program.