Search is best done by automatic indexing. But indexing cannot always
"understand" the data format, e.g. pictures, in which case tags are
useful. Indeed tags might be used even when mostly dealing with text
files, because

a. There might not be any indexing software available

b. Tags might help add information to pages which wouldn't normally
have the tagged word

The search functionality in this box is purely by user-specified tags.
(maybe google will help you out if
you're wanting a more generic indexed search).

The most common tags used to tagged pieces of information are shown below: