Make sure you have your phone set to allow app installation from unknown sources. It is a checkbox under Settings > Applications. Then you should be able to install Z4Root by going to your file manager and selecting the apk. It should give you an option to open it in app manager and then you can install it.
Once it is installed, you can root by clicking the root button in the app. Once you are rooted, you need to click the "Bootstrap Recovery" button in the bootstrap app. That will install the recovery. You can't do that without being rooted.
Once you have rooted and installed bootstrap recovery, you can install a ROM. If you tried to install this theme on a Motorola ROM, that is why you went into a boot loop. Themes are meant to be installed on specific ROMs. Some are compatible with others, but most are not. You can install liberty by following the instructions in the Liberty 1.5 post in the Liberty subforum. Just search for Liberty 1.5 and it will find it.
Once the ROM is installed, then you can install the theme. There are also other versions of my themes for other ROMs. I support RubiX, Tranquility, GummyJAR, and Liberty. They have their own posts, but you can browse the posts in my subforum to find them. I am dabbling with Fission right now and may support it soon as well.
We are a very helpful community, so let us know if you have more questions. Read the thread stetsonaw pointed to. It should elaborate on what I have said and give you a better understanding about what the steps are and what they do.
