Newcomers to GNU, Linux, and BSD Operating systems will want very specific instruction regarding the installation of an operating system for their own specific PC, Laptop, or device. However many variations exist due to the variety of Bios, Uefi, and other similar systems. Fortunately the process doesn't change much and this guide can act as an overview to the process itself. This process is almost identical to installing to SD card, but SD cards require an .img file rather than an ISO. A tool called win32 disk imager is preferable for writing to SD cards. This process from Linux requires slightly different tools but those tools exist on the Linux systems themselves i.e. USB image writer on Linux Mint vs Rufus etc.
Downloading The Media
Whether you are looking for Ubuntu, Linux Mint, Debian, Red Hat, or have no idea what any of that is but desperately need a Linux OS for your system you'll need a specific OS to download. For this example we'll be using Linux Mint 18.3 with a Cinnamon Desktop. Select a location near you to begin the download which should take about 20 minutes on average.
Preparing The Installer
In this example we are using a USB thumb drive as an installer, after the installation is complete the thumb drive can be restored to normal function but creating the installer will remove anything previously stored on the drive. From Windows we'll use a tool called Rufus to create the installer. Once downloaded, execute the rufus file to open the installer creation menu, click the little box that says ISO and from the resulting menu find the Linux Mint ISO you downloaded. (Probably in downloads.) You'll be reminded that the installer will destroy everything on the drive, select proceed and wait the 5-10 minutes for the USB drive to be converted to an installer. *If you are installing to the same device upon which you created the installer, leave it where it is, but to install on a different machine, remove the installer.
Installing To PC Or Laptop
Turn the computer completely off and insert the USB - power on and interrupt the bootup process by pressing either F10, F12, or whichever is prompted by the bios screen. From within the bios select the startup order list and move the USB device to the top. This is often done with odd controls listed on the right in a box. Sometimes the usb will be listed by manufacturer, sometimes as USB Hard Drive, etc it will never be listed as CD, HDD, or Lan. If you are already using Windows 10 you may need to enable legacy boot to even see this prompt. Once you see the Rufus prompt press the spacebar (during the countdown) to boot the Linux. From within the desktop menu of Linux Mint (or whichever Linux you are using) select the install option from the desktop* after connecting to the internet. It is preferable to do the installation via wired connection, but via Wifi is fine, just a bit slower. If your machine doesn't see the Wifi use a wired connection or tether via smartphone to continue. The installation menus are self guided. After the installation be sure to power the machine completely off, and expect a few hiccups until the second reboot, i.e. Wifi drivers etc upon an installer prompted restart are often not loaded correctly, restarting a second time usually fixes this.
*On some Linux OS the installer option is in the menu system rather than on the desktop, prompting some exploration.
If You Don't See The Rufus Or The Linux Menus
If you didn't see a way to boot from USB device in Bios, take your time and recheck the options marked startup. If you see a uefi option, you may need to enable/disable it depending on the Linux variant you are using.
If you managed to get to the installer but couldn't connect to Wifi and have no wired option, you may want to try a different variant of Linux altogether, i.e. Bunsenlabs, Suse, etc. Some have better hardware detection on legacy systems than others, but generally once installed any of them can be made compatible with a working internet connection.