Those are done with steel or wood rods drilled into the studs. There are some holes on the back side of the shelves that accept the rods for the support.

eleena, here's an older thread with several different types of floating shelf supports, including the one that KentWhitten posted.

Here is a link that might be useful: floating shelves

Thank you!

That is exactly what I as looking for. Before posting, I Googled it but found mostly DIY recommendations that were not very useful to me.