LÖVE runs the contents of a folder if it can find a main.lua in it (Like Bill said).
[Note that it doesn't check subfolders].
There are three ways to run a love2D program, you can:
a) Drag the folder over the love.exe binary/link (This works in Win and *Nix, I don't know about OS X).
b) Navigate to the directory that is one level above the folder and type love [folder containing main.lua]
or
c) Zip it up and rename the .zip to a .love. Then double click the .love file
Option 'b' will fail if the binary is not in the %PATH%(Windows) or $PATH(*Nix) variable
(It will spout an error message like 'love' is not recognized as an internal or external command, operable program or batch file. on windows and bash: love: command not found on linux).
There are two ways to solve this:
(Both require ADMIN/root privileges, )
1) Add the love binary to the PATH variable. Here's how to do this in windows and in linux (In linux you want to do something like this: PATH=$PATH:$HOME/where/ever/you/put/love/)
2) You can add a link to the love2D binary in C:\WINDOWS\system32 or /usr/bin/.
In windows you create a shortcut to the love.exe (wherever you installed it to) and then drag it into C:\WINDOWS\system32. In linux you can run this:
sudo link /path/to/love/binary /usr/bin/love && sudo chmod ugo+rwx /usr/bin/love
I hope this helps!
Sources:
Google (the links above), Love2D and my knowledge :D