Downloading Drupal locally provides a safe place to experiment with code without affecting a live site or exposing confidential site data to others. This lesson will set up a local web server on a computer, and install Drupal on that web server.
There is a short video, Install Drupal Locally with Dev Desktop, that walks through this lesson.
This lesson assumes access to a computer with a Mac or Windows OS. If you are on Linux, you can install a web server appropriate to your distro. You can watch a video on installing a web server on Ubuntu. Note that if you are using Drupal 8, you will need at least PHP 5.4. On ubuntu, it is recommended to use Ubuntu 13.10 which ships with the required software versions by default (see Ubuntu 13.10 installation instructions)
This lesson has 3 sections:
Note that these instructions use Dev Desktop, but there are other all-in-one web servers you can use, notably MAMP for Mac (Installation video) and WAMP for Windows (Installation video). On Linux you will need to install a web server based on the distro you are using. If you would like to have an entire virtual machine instance, with lots of other web server goodies, you can check out Drupal Pro or Drupal Quickstart or do it manually following these instructions from klausi.
If you have a web server already, you can follow these instructions from section 2: Download Drupal 8.