To get the most out of your purchase of PowerStore, you will probably want to upload it to your live server, install it, and see what it has to offer. You shouldn't go through the challenges of setting it up locally unless you need to make modifications right away. Many users quickly discover that PowerStore provides so much, there isn't much customization to do.
It really is that easy if you do not need to modify any of the functionality. However, you're entering the realm of web development if you choose to modify the product's features. That will obviously require more steps (and probably some learning). Needless to say, if you upload PowerStore 3 to your live server, there isn't much more to do than set it up, and add your products.
Most newbies do not require any more than PowerStore already has to offer. So, i would suggest getting it installed on your live server first. Then, if you find that you do need to modify something for whatever reason, you will want to install it locally. At that point, you can set up a local version for making your own modifications to. This can be done by downloading your live version to your local testing server, or repeat the Installation Wizard locally. Personally, I'd suggest downloading your live version to your local machine - but that is your call.
The link Eric provided is a tutorial which contains a video of the same steps covered in the tutorial. Although the video was recorded on a Windows machine, the steps are the same for the Mac. Reading the steps may be more beneficial as there may be useful notes regarding OS X that aren't shown in the video.