The translations are broken up into two separate pieces.
Interface
The interface mainly consists of menus and labels.
The interface can now be translated by following these steps:
Log in using the login button at the top
Click the black button in the bottom right
Search for the untranslated string that you wish to translate by using the text box that has now appeared in the bottom left
Type your translation in the bottom right text box.
When you have finished your translation, click "save translation", the furthest left button in the right column.
Content
Content is anything that is a node in Drupal. Nodes include book pages like this page and materials. Nodes are the main content of the site, so these are the most important to translate.
When translating materials, new translated files can be attached to it.
Translating content is easy.
Sign in or Create an account
Navigate to the specific node or material you wish to translate
Click the "Translation" link at the top
Click "create translation" for the language of your choice