Find the file you downloaded and right-click on it. You should get an option to "Extract All...". Click that, and it'll open a series of windows that just ask you where to extract it.
After it's extracted, you should have a directory with all the Habari files in it. Then you'll need to get them uploaded to the web host you've paid for. The easiest way to do that is usually FTP, but a lot of shared hosting services also include a web-based file manager that you might find easier for this first time. That'll depend on your host, and I'm sure they've got some instructions for uploading files in their Knowledge Base or Support area - they always do.
After that, you should be able to load the domain you reserved and the Habari installer should appear. There should be instructions on the wiki and in the built-in documentation for that, but feel free to ask questions.