May be you have searched this term before but got tired of reading very long solutions then this is the right place for you to do it quickly.
Warning: If you have UEFI secure boot then please disable secure boot/UEFI from BIOS then proceed.
Note: I suggest you to make your root partition a little larger such as (30 GB) if you want to install large softwares such as Android Studio or any other.
Step 1: Getting Prepared
Prerequisites:
a) A PC running Windows 7/8/8.1/10 , with at least 30 GB of free hard-drive space.
b) Blank DVD or USB
c) An external Harddrive big enough to backup your Windows installation. I recommend it if something goes wrong you have backup from which you can recover later. But if you follow instructions thoroughly then you will face no problem.
Step 2: Select a Linux Distro
There are many distros of linux i suggest you to start with "Ubuntu" then i will give you more info about distros in another post later. Just start with ubuntu i myself started with Ubuntu.
Step 3: Downloading Ubuntu
Go to the ubuntu website, https://www.ubuntu.com/download/desktop
Latest version is "Ubuntu 17.04"
But i recommend you to use "Ubuntu 16.04.2 LTS" as it is the most stable version of Ubuntu.
Just go with 64 bit.
Step 4: Prepare Installation Media
You can directly burn the downloaded image to a blank DVD and boot it but if you want to use a USB drive, you'll need the program "UNetbootin" which is available here: http://unetbootin.sourceforge.net/
Just go with UNetbootin i'll give more alternatives to you later in another post.
Step 5: Partition the Hard Drive
Simplest and Safest way to do this is to do this process with Disk Management tool which is present by default in Windows.
Step 6: Restart your PC and plug in the USB/DVD which contains Ubuntu.
Step 7: Boot into removable media this option may be different for some users.
Step 8: Now your Removable Media must boot and it will show Ubuntu Desktop.
Step 9: GRUB Option
It will show a option to install GRUB (Grand Unified Bootloader) select "Yes/Ok" and select your hard drive name if it gives option any option otherwise it will just complete the process.
Step 10: Now just shut down and remove the installation media (DVD/USB).
Step 11: Select your OS
Now start your machine it will show GRUB (Grand Unified Bootloader) and several options as shown below and select the OS you want to work.