This is the most easiest step. You have many possibilities for finding the answers for this case.
1 - Using the forum search engine, since this has already been posted several times in the past.
2 - Using the developpers tool kit from the admin section - > tools menu.
3 - To read the PDF Documentation's FAQ - posted and announced by DrByte, since the new forum interface has been released.
4 - After installing Zen Cart for the first time, the index page directly specify where specific text are located - within specifc files (when using the template_default one of course).
Personally, the quickest solution would be no 4.