A portal is just that, a portal. It is a gateway to other sites and
information. It is geared for large audiences and static content. It
can be used as a launch pad to access all of your other more detailed
information.
A team site (the product term is Windows SharePoint Services [WSS]) is
for small team collaboration. It is geared for small audiences and
short term content. They are excellent for online team, meeting and
document collaboration. They are expendable and can be nested and
grouped into collections. They allow for list, library and site level
security.
A portal can seemingly pull all of the content under one umbrella
through SharePoint search.
Does that help at all?
About the files, both portal and WSS site pages are generated by
templates. Those templates are physical files that reside on the web
server in a common directory and are treated the same. When you create
pages within a portal or WSS site, that page is based of the template,
but the content data is stored in a database. For every page in a site,
there is not a directly related file sitting on a server somewhere.
Everything unique to that page is stored in the database.