Finding a file in terminal

One way is to use "find":

find / -name filename

type man find for more options. more info about find command

Another way is to use the command locate:

updatedb (as root)
locate filename

Use whereis and which to find a program:

whereis programname (locates binary, source, and manual page files for a command).
which programname (locates a command).

The man whereis and man which commands provide more information.