not sure what you have done but this will work.
When you create your domain name you will have a directory normally called htdocs which holds all the files. This is the root. when you type in www.domain name the webserver will call pages in a preset order normally index.htm, index.html, index.php without you typing in index.....
Unzip your download package into a directory on your development PC then using any ftp client upload the unzipped files to the root directory ie into htdocs.
One of the files is index.php
Once you have copied all the files and directories into that folder open your browser and just type www.yourdomainname.com
The code will pickup you have not installed before and will automatically open the install wizard. From there just follow your nose and it should all work.
Do not put the files in a sub directory of the htdocs ie htdocs/powerstore, whilst it can be done it can reap havoc with files paths etc and unless you are either a fantastic patient coder or a masochist I'd leave well alone.