Get a Linux Distro to Install
This example will use the 16.04 distribution of Ubuntu Server. The procedure will be generally the same no matter which you pick. I've been installing Ubuntu Server software on various machines for a decade or so. It's always the same routine, except I used to do it with CD-ROM's, but now it's always done with a USB drive.
Getting back to the point... Use that link above to download a server ISO file. After you've done that, you'll find an ISO type of file in the folder that your browser download files into. The filename represents the version you picked.
Special note: The filename will have "amd64" in it and you may panic a little because you have an Intel processor instead of an AMD.
No need to fear. That's a concern I used to have. It's a legacy notation thing. It's an artifact from the time that AMD stopped copying the Intel processor and also did 64 bit processing as a rule. Because they became different kernel architectures Ubuntu would always have to program i386 and AMD64 options. Now, if your Intel chip is a 64 bit system, you install the "amd64" version on it.
This ISO file you have is an image of a bootable hard drive that has the special purpose of installing a operating system, but like your physical image in the mirror, it does no work so you need to make a real version of that image file. What you have to do now is take that file and either a blank CD-R or a USB Drive and make a bootable removable thing to stick into the computer you want to turn into a server.
On Ubuntu Linux their's always a program called "Startup Disk Creator" to accomplish the task. Have that USB drive in your workstation that you downloaded the ISO on, and search your Dash menu for the Startup Disk Creator program.
Note: Initially I was going to do a 17.04 server install but it failed on the first try so I gave up and made this a 16.04 tutorial. Looking closely at the images below show that I got screenshots while setting up for that.
Typically the Startup Disk Creator program will find the ISO, and it will find the blank media you can put it on. You just have to click "next" a few times. If all goes well, it will finish and notify you. You may lose site of the completion message if it's behind another window. That can happen if you multitask while it's building the bootable media.
Your media device get's renamed to the Distro you put on it. This means you are done with the preparation and are ready to stick that new media into your server to be and run the installer. If you don't have a Ubuntu Workstation, you can still make a startup disk on Windows or Apple, but I'm not going to explain how.
Note: if the computer you're putting this on doesn't know its supposed to boot the USB device, you won't get anywhere. It's the BIOS of the Motherboard that has the settings to alter that so you can boot from CD-ROM or USB Device. Consult Google about how to change the BIOS for your particular computer. Usually you have to press [Del], or some Function key on the keyboard after you power it on, and you have to do it before any hard drive loads an operating system. On some systems you will see a key option for a "Boot Choices" or "Boot Options" and if you press that key you won't need to tinker with the BIOS, you'll be given a set of choices and you just pick the one for your method; USB or CD-ROM.