You don't really "import" your own website into eZPublish.
Instead, you normally start with a model website such as Website Interface, then modify that site to have the structure, content and style you want. You can also start with a Plain Website, but I wouldn't recommend that for your first site.
The following links (from Education->Articles) are useful to get started:
If you need to import lots of content easily you can use rss import or one of the many extensions here on ez.no and / or projects.ez.no.
eZ Publish can host several websites both in same database or with separate databases, but it's not something you can use out of the box without some modifications to the style and templates. But this depends on what you where thinking, ezwebin does support several sub sites on one install, but then they share design and site settings (basically you use css to have slightly different styles on the different sub sites). So what where you thinking of ?