Up through Windows 7 you booted into Safe Mode by smashing the F8 key during the boot process. With Windows 8 or 10 it is different and "slightly" hidden. You can continue to try the F8 key, but you won't be successful the majority of the time. One way to get to safe mode is via the Windows recovery environment. If you can boot Windows normally, an easy way to get to the recovery environment is to hold down the Shift key and click on Restart. Another option is to press the Windows key + I to bring up the Settings app. Select the Update & Security option. Select the Recovery choice and click on "Restart now."
If your machine is so screwed up it won't boot normally, you should be presented with a "Recovery" option after two failed starts. There are other boot options too, which you may encounter. See the referenced post to see how to deal with those.
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Digital Forensics/Information Security/Information Technology