Yes if you're grinding your teeth at night then a mouth guard will certainly help prevent damage to your teeth when grinding your teeth.
It can take a little while to get used to using the mouth guard when sleeping because they can be uncomfortable at first.
But after you wear the mouth guard for a week or so at night then you should get used to it.
I used to grind my teeth at night and I did start using mouth guards to protect my teeth from damage and they did work.
I was still moving my teeth at night but the mouth guard helped protect my teeth from grinding of the teeth.
You can buy some mouth guards for teeth grinding on Amazon or other online stores or even in Walmart Stores for pretty cheap and they're well worth it.
Sometimes stress and anxiety during the night can cause teeth grinding as well so avoiding stress and trying to get rid of the anxiety can help with your teeth grinding.