Wikipedia gives a short history of Linux. A list of some of the more popular versions for 2015 together with their relative virtues can be found here.
Until the development of Windows 8, it was relatively simple to install Linux distributions from a DVD or from a USB stick on computers that allow booting from a USB stick. I use Lili USB creator to create mine but there are several other free creators. The instructions are easy to follow. Once you have your USB stick or DVD with the Linux installer and distribution on it, you simply use it to boot up your computer into the Linux OS.
To do this it used to be easy before Windows 8. You simply went into your BIOS settings by pressing a designated key when booting. Often what key to press is shown during the bootup process. You can then change the boot order so that the computer will boot from the USB stick or DVD. There will be a list of choices. Some computers will not have the USB alternative. You then restart your computer and it will boot into Linux. You have the choice of just running Linux from the DVD or USB-stick, installing Linux alongside Windows (dual boot) or wiping out your Windows and installing just Linux. Newer distributions often also allow you to run Linux from within Windows.The installer has a program that will help you partition your hard drive but this can also be done within Windows 10 and perhaps earlier versions. A good account of how to install Linux in a dual boot system can be found here.
With the advent of Windows 8.0 and 8.1 and Windows 10, the traditional BIOS sytem was changed to a UEFI system. However, you could still access the UEFI settings so that you could set them to boot from your DVD or USB stick. Accessing the UEFI settings is a bit more difficult than with the earlier or legacy BIOS setttings but there are at least different ways of doing it Three ways are described here. However, since Windows 8 there is another problem, UEFI Secure Boot.
UEFI Secure Boot is described a follows:
When you boot a new Windows 8 PC, the Secure Boot feature in the UEFI firmware checks the operating system loader and its drivers to ensure they’re signed by an approved digital signature. On Windows PCs, the UEFI Secure Boot feature generally checks to see if the low level software is signed by Microsoft or the computer’s manufacturer. This prevents low-level malware like rootkits from interfering with the boot process.But the same feature that blocks rootkits will also block other software, like Linux boot loaders. This created a huge problem for those who wanted to install a dual boot system or just try out Linux from a DVD or USBstick. The system refused to boot because there was no Microsoft or other approved signature.
However, there was a work-around to this problem. There was a switch within the boot settings to turn Secure Boot off or on. Turning it off allowed Linux users to boot the system into Linux. Microsoft required that Windows 8 have this switch. However, in Windows 10, Microsoft had a surprise. Having the switch became optional:
Manufacturers will be able to enable UEFI Secure Boot without giving you a manual kill switch, as they have to do with Windows 8 systems. If that happens, you’ll only be able to boot Microsoft-approved operating systems on these locked-down PCs. Microsoft is turning the Secure Boot screws tighter, and Linux users are right to be concerned—but the issue is more complicated (and probably less disastrous) than it seems at first blush. There are still some Linux systems that are able to boot even though UEFI Secure Boot is turned on, including popular versions such as Ubuntu, since they have an approved signature. However, many versions will not.
I tried booting Linux Mint from a bootable USBstick with my HP Pavilion P6 series computer running Windows 10. It failed to boot. I checked to see if there is a toggle switch to turn off Security Boot. There was not. I then went to my Gateway SX2185, also running Windows 10, and found it had the toggle switch and I turned off Secure Boot. I was able to run Linux Mint with no problems. I then created a bootable USBstick for Ubuntu 14.04.3. I tried to boot from it on the Pavilion. It works fine. Microsoft has not stopped users from trying Linux or creating dual boots. It has just made it more difficult so that less people will be bothered. Readers could carry out a little experiment. Go to your local computer store and ask them which of their computers have switches to enable or disable UEFI Security Boot. It would be interesting to see how many sales people know what you are talking about.