Your main page should be called index.html, so that when someone points a browser to www.yourdomain.com, that's the page that comes up. But you can create as many other pages as you like, with different names. So, you could have a page about dogs called dogs.html, a page with contact info called contact.html, and so on. Then you just put links to those pages into your main page:
<a href="dogs.html">Click here for the page about dogs</a>