I believe updatedb is intended for updating the locate database, allowing the 'locate' command to find files quickly. Aside from that I don't think it has any purpose.
So, you'd run 'updatedb' after installing a bunch of stuff, so the next time you run 'locate' it will be able to find those files.
In order to use the commands anywhere, you would need to add those paths to your profile. To find out what your current path is, type:
To add other stuff to it, it's something like:
(varies depending on what shell you use). Look for some shell HOWTOs, I am sure they will get you going