Ehm.... if you want to use them on your phone you might want to check the gallery if they are uploaded (most are) and just download them. Once downloaded, you can open them directly in Theme Creator as each .thm (theme) file already consists of all the 'smaller bits and pieces' that are described in theming tutorials.
If they're not in the gallery just contact the author and ask them, I'm sure they'll be more than happy to share

Now if by 'using the theme' you mean taking it, ripping it apart and making something new....... I guess that's up to you, but be sure to let the original author know and give credit where it's due

Good luck