One possible use of gpg is to encrypt files.

I've had amusing uses for it.

Encrypt
$ gpg -c myfile.txt
(outputs myfile.txt.gpg. you may then wish to
$ rm myfile.txt
which deletes the original file)

Decrypt
$ gpg myfile.txt.gpg

You may also wish to rename the file after encrypting it ( $ mv myfile.txt nothingtoseehere but it may prompt for a rename of the output, you can simply press enter to keep the old/default filename)

EDIT: james174's idea is...much less secure than gpg (and don't kid yourself there either). On linux the CLI equivalent would be to rename the file or folder with a dot/period prefix, as in .documents This isn't real security and meant to keep directories "pretty".