question about headers + tables

Are you allowed to put a table inside a table?
On W3schools it says that all 6 headers must be used in order.

So would this be allowed?
<div class="nav">
<h1>Navigation</h1>
<h2>Sub Header</h2>
</div>

<div class="main">
<h1>Welcome...</h1>
<h2>Sub Header</h2>
</div>

Are you allowed to put a table inside a table?

You don't have any tables in you question so I think the real question is about:

On W3schools it says that all 6 headers must be used in order.

What you do show in your <div>'s is correct. You should usse H1 and then H2 But you dont have to. It's not a law, just easier to read.

The code you supplied does not have any tables in it. Usually you should only have one h1 tag on a page.