Modern versions of Office (Word/Excel/Powerpoint) include a feature called AUTORECOVER which you will already be using and saves a copy of file(s) you are working on every few minutes (standard setting is every 10 mins but this can be altered).
This is not a substitute for regularly saving your work by clicking Save. Manually saving your file is the surest way to preserve the work you have done. Click the icon or do Ctrl + S. It only takes a second.
Autorecover saves to a separate location and includes other information like your workspace (eg if Excel crashes, autorecover will 'remember' what files you had open and how the windows were arranged).
If your PC crashes while you are in Word, Excel or Powerpoint then the next time they open, the program will attempt to open the autorecover versions of any files you were working on.
Note that the original file is not altered by autorecover, to save back to that you need to do so yourself as above.
Why isn't there just an autosave function so Word/Excel/Powerpoint can save my file for me?
Some more information on this topic is here from Microsoft -