Because Linux itself is a kernel and not an operating system, it is not possible to download a copy of it. However, you can download a Linux distribution such as Ubuntu or Linux Mint. Both are available for free on their respective websites.
Ubuntu is a popular comprehensive Linux distribution that comes with the basic tools that a home user needs, including an office suite, a Web browser and media applications. It is an open source operating system, meaning that any developer can add new features to it. It has a built-in firewall and virus protection software.
If switching from a Windows computer, Linux Mint is an alternative that is easy to adapt due to its similar interface. The operating system is highly customizable and features a Menu similar to the Start Menu on Windows. Likewise, it has a taskbar and a system tray. The developers claim that the operating system supports over 30,000 applications, as of 2015.