This section is an amalgamation of some very different programs, which are united under the eponymous purpose of "finding stuff," but work in quite different ways.
Generally speaking, find (the biggie), searches the directory tree for a file or files specified by the command line. This happens to present a golden opportunity for hard-core programming in that it is a real world example of a classic computer science problem. As such, the find command has quite a few options and is perhaps more complex than necessary. For those of you simply wishing to learn the location of a particular file in a timely and painless manner, I recommend locate.