[Nexus 5X Q&A, Help & Troubleshooting] fast69mopar:
[MENTION=7450184]starlitserenity[/MENTION], I can help you get an OS back onto your phone. It's very simple even though you may be a NOOB. It's OK. As long as you have access to a PC and Internet you are OK because you can still access TWRP. Here is a list of steps:

1) go to xdaforums.com/nexus-5x/development

2) scroll down to the ROM labeled

"Pure Nexus"

3)In the first post (Original Post), scroll down and click on "Downloads & Changelog" You will be redirected to AFH (Android File Host) to download the ROM/OS

4)Scroll down just a little and you will see a Green Box with files/ROMs. Click on the newest one labeled

pure_Nexus_bullhead-6.0.1-20160407.

After you click on the ROM file, a new screen will appear with a Green Box that says "Begin Download".

5) Click on " Begin Download"

Once you click the "Begin Download" box, you will see below another Green Box that says "primary download". Click on the " Primary Download " box to begin downloading your new ROM/OS.

6) Go back to the Pure Nexus original post/first post and click on the link labeled "Highly Suggested Gapps"

You will be redirected to Android File Host again to download your Gapps(GoogleApps). Scroll down just a little to the Green Box again and select

PureNexus_Dynamic_Gapps_6.x.x_4-7-16.zip and click on the link.

7) A new screen will appear with a Green Box that says "Begin Download"

Click on the "Begin Download" box and just below another Green Box will appear that says "primary download".

Click on the " primary download " and this will download you Gapps.

8) Once both of your files have finished downloading onto your PC, boot your 5x into TWRP and connect it to your PC and let the drivers install so your Nexus is recognized by your PC.

9) Now that your 5x is recognized by your PC while booted into TWRP, you will need to move the 2 downloaded files from your PC's download folder to the internal storage of your 5x.

10) Now that you have moved both downloaded files to your Nexus 5x internal storage you will need to reboot your recovery. Select the home button in TWRP, select reboot, then select reboot recovery to reboot TWRP. This will all TWRP to recognize the two new files that were moved to your Nexus internal storage.

11) Unplug your Nexus from your PC. On your device, go to the TWRP home screen and select wipe, then swipe to factory reset. Now you are ready to install your new ROM and Gapps

12) Now that you have wiped the 5z again, select the TWRP home button. Next, select "Install". Navigate to your SD card/internal storage to locate the two files we moved to your Nexus from your PC. Select the file that says

pure_nexus_bullhead-6.0.1-20160407

Once selected you will be directed to a new TWRP screen and you will see a box to click on that says " Add More Zips" Click this box and navigate to the SD card/internal storage and select the 2nd file that says PureNexus_Dynamic_GApps_6.x.x_4-7-16.zip. Once you have selected the file you will be directed to another TWRP screen with a swipe button to install the ROM file and the Gapps file. Swipe the button to begin the installation.

13) Once the installation is complete, you will see a box that says wipe cache/dalvik. Select this box, wipe cache/dalvik, then select reboot system.

14) Once your device boots you will proceed to the setup wizard just like when your Nexus 5x was new out of the box. Go through the setup wizard to setup your device and once completed, reboot, and you will be back to normal with a pretty sweet custom ROM called Pure Nexus.