My MAC keeps restarting and will not allow me to do do anything

If the update continues to fail, power down your Mac completely (hold down power for 10 seconds) and when powering back on, hold down the "Command" and "R" keys. You will be greeted with a "macOS Utilities" page. From there, select "Reinstall macOS". With reinstalling macOS, your data will remain intact, but a fresh copy of your operating system (macOS) will be installed. You shouldn't encounter anymore issues from there. Below is the Apple help page for reinstalling macOS.

https://support.apple.com/en-us/HT204904

If the error message states "Your computer restarted because of a problem", then you're experiencing what is known as a kernel panic, which is a separate issue.

https://support.apple.com/en-us/HT200553

Try booting into Safe mode

http://support.apple.com/kb/ht1564

This will not load any 3rd party additions, it will load some more conservative Apple drivers (may cause screen flicker), and it will clear some kernel caches (a cache is saved data in a form that can speed up a program, but is totally redundant to the original source, and thus can be safely cleared).  Booting into Safe mode is just an experiment, but can frequently eliminate any 3rd party interference, or a cached item out-of-sync with the world.  (Verify Safe mode via Applications -> Utilities -> System Information -> Software -> Boot Mode -> Safe vs Normal)

See if you have a panic report (file's ending in .panic).  If you have more than 1, please post a couple as the differences can be very useful:

Look for the Kernel Panic reports at:

Finder -> Go -> Go to Folder -> /Library/Logs/DiagnosticReports 

<http://support.apple.com/en-us/HT200553>

The panic report should have ".panic" in the file name.

You can put the panic report in an "Additional Text" box when you Reply

If, AND ONLY IF, you have difficulty posting via "Additional Text"

then try posting to PasteBin.com, and give us a PasteBin URL link.

<http://pastebin.com/>

Are you currently updating your macOS firmware?