Despite the excellent resource already posted, I will go ahead and leave this. Please tell us first which OS you are trying to use to install Pure OS onto USB Thumb Drive with. I am guessing it is likely Windows 10, in which case.
Supposing that is the case, I would first download the “Universal USB installer” software to do the work. I think there is a ban on outside links here, so I will not provide link. The Pure OS site describes their version of doing this, and recommends Etcher for writing to the USB drive. Etcher seems to work the first time, and later attempts to do install with it have issues (my experience). I am sure the more knowledgeable here can tell me what I am doing wrong. No doubt it is an issue with how Windows works with USB drives, as Windows does not play well with others.
Download a copy of Pure OS onto the drive. https://pureos.net/download/
Verify the SHA256SUM: with some type of hashing software. I use “MD5 & SHA Checksum Utility 2.1” which is an older program, still works.
If you now start the Universal USB installer, It will give you options. Where it asks which version of Linux you will be installing, I go very near to the bottom and choose “Try Unlisted Linux iso.” I do not think it effects the install in any way no matter which of these you choose. Choices in UUI feel obvious from then on.
You will then have a Live version of Pure OS. While still in Windows, I would the text editor to create a little file to save onto the file structure of the USB which is saved with the name and version number of the OS you are using. Such as “PureOS 8.0 “Prometheus” Beta 1”. I have like ten different USB keys of Linux, and it is useful to be able to look at the drive and know which version of Linux is on it.
One can, hopefully start this USB key by going into the BIOS/EFI of the computer and directing it to start from the USB key. That is, one powers down the computer from the start button on the lower left side. Presses the power button on, while pushing the correct function key to get it to start into the BIOS/EFI, every two seconds, do not hold the function key down. Every manufacturer is different, mine is like either the F2 Key or the F12 Key. Likely a little message will flash by that tells you which key you should have been pressing every two seconds, if you can read that fast.
Write a note to yourself as to what you changed. I do this part strangely, I disable the UEFI, and then the Security options, (which then resets itself to “Legacy”) I admit this is odd, on my computer this steps around the “Windows Boot Manager” and it automatically defaults to starting from a USB key. One can also, usually find a combination that allows one to point at the USB key with Pure on it. I think the Pure OS has the UEFI key installed. I use some Linux versions that do not have a UEFI key (or whatever it is called) to use the Intel UEFI.
You should be able to, hopefully start, the live version of Pure OS. If you see a message about the hard drive is unstable, or some such nonsense, well this is another Windows 10 Issue. You have go back into Windows 10. Windows 10 does not play well with others. M$ intends it that way. In this case, M$ built into Windows that it does not actually do a full shut down of the hard drive when it is powered off. The hard drive is actually put into “Hibernation Mode,” This allows for a faster start up of Windows, and this error message about do not proceed further or you might damage drive. What you must change is inside Windows itself. The little gear/cog that is second up on the Windows start menu is Settings. “Settings/System/Power” Then, oddly different manufacturers vary where the tab is to do, “On ShutDown/Advanced Settings/” Tell it to explicitly shut down the hard drive on Shutdown, in place of “Hibernate.”
Now you have to consider whether you have backed up the computer, and how much trouble you are going to go to the attempt to Install goes sideways. For sure, save all the logins and passwords you have, Registrations for software and such. But it is up to you.
Now you will see M$ has a bunch of Partitions you may not have realized were out there. If you modify any of those Partitions in any way, Windows will pitch a hissy fit when you try to start it again. I do not know how to recover from all the possible complaints Windows may have if something is different than how it left it.
You are only concerned with the M2 you put in, and modifying the boot so it will start from where you want it. Some versions of BIOS/EFI are generous is allowing you to do such without requiring you to do something to the Boot Partition that Windows has. I am not qualified to speak on this. Be very wary of which partition you Format and install Pure onto. It is easy to make a mistake.
One can create an installed version of Pure, (not the Live version. Usually Live versions will not keep modifications you make to them, installed versions of Linux will. Installed versions require that you enter your own Passwords.) Problem being that doing an install from USB Flash Drive to USB Flash drive still might allow you to blow up your hard drive, and it is (so I am told) truly a bad idea to overheat the USB system of a computer as you would in trying to install USB to USB).
What you could do, as you seem willing to open the laptop. Go back in, unplug the battery, and unplug your hard drive that has Windows. Plug battery back in, close it up. Then you can not accidentally clobber your Windows Drive doing an install. Doing a dual boot later is another problem.
Actually the best thing you can do now, is wait a day or two so some other folks here, who are more knowledgeable than myself to tell you what stupid things I suggest here, and how to do things correctly. This gives you time to back up, save mutliple copies of what is on your hard drive.
AOMEI has a Partition manager and a clone of hard drives software. I dunno whether it is good to trust it. I am using a 2016 version of Acronis, which does cloning. If you have either a Seagate or WD drive involved, Seagate has software for cloning and such. Might not want to work with M2 though.