Joomla 1.7 includes a basic way to implement a multi-language site. This doesn't replace other multi-language content management like, Joomfish, for example. You can find a complete list of these in the JED.
What you can do is activate the language switcher module, and let visitors switch the joomla core labels and headings to their preferred language. You will need to download and install specific language packs for each language you want to use. You can find the language packs in the JED.
It's quite difficult to understand therefore we got a nice video to show how it works step by step.