Hi Patricia,
The first thing you should do is Google the subject of your post "multilanguage portal site:dotnetnuke.com". You will get several results that will give much more information than the following:
1. You have installed a Spanish language pack. That language pack translates the DNN application's interface. That is, menus, module options, settings, email texts, etc. It is not a minor thing, there are nearly 10,000 resource texts in a standard DNN installation.
2. The "dynamic" content, that is, the text that you write on your site, such as your news, editorials, and so on, has to be managed using third party tools. You will find plenty of references to them on this forum. Many are for free, some have to be paid for. DNN's roadmap includes localization of dynamic content somewhere in the near future, we all hope so.
Using these third party tools (mostly modules), you will load the content for each language and the modules will change automatically when the user selects another language.
Go for it! Good luck :-)
Saludos,
Alejandro.