The Van Beuren's Tom and Jerry is in the public domain and not copyrighted.
However the other Tom and Jerry is copyrighted and not in the public domain as of now.
That is the Tom and Jerry with the cat and mouse created by Barbera and William Hanna are not in the public domain and are copyrighted.
So if you upload Tom and Jerry Cartoons to Youtube or try to sell it or copy it then you could get into trouble for copyright infringement.
There are a lot of Tom and Jerry Cartoons to watch on Youtube though that are legally uploaded.
So if you want to watch Tom and Jerry online you can watch them for free on Youtube.