This is an old reupload from youtube, I made it years ago when I was figuring out computer stuff. I'll admit this probably isn't the best explanation of a hash, but it's simple enough for the layman to understand.
I missed one crucial point. An important defining characteristic of a hash is that, currently, computers are not powerful enough to reverse a hashed file to see what the output came from. It's a "one-way function". This is why hashes are used because they can provide cryptographic proof that data either has or hasn't been altered.