When spell check puts the red underline to show a spelling mistake, right-click and choose “Add to Dictionary”. Then the Spell Check feature knows to ignore the specific words. If they are actually getting auto-corrected (rather than just tagged as spelling errors) then you will need to add them into Auto Correct. Depending on the version of word you are using – it will be the Office button or File tab that you choose, click on Word Options –> Proofing and there sits your Auto Correct Options. Under the AutoCorrect tab, click on Exceptions and add in anything you don’t want corrected.