There are two basic steps: downloading the software, and then actually installing it. 150M people have iTunes (and also QuickTime) installed--it's not difficult.
Before clicking on this link to download the software, bookmark this page so that you can come back to it once you're through downloading.
Download the software from Apple's QuickTime download page.
Make sure to take note of where you download the software to on your system, and the filename of the download. You will need to know the location in order to successfully complete the next step.
Find the location on your computer's disk where the software was downloaded Launch the installer that was downloaded in the last step. The installer is also known as setup program.
Follow the instructions of the installer to complete the process.
You may need to reboot your computer--if so, the installer will notify you.
If you have a newer Mac that doesn't have QuickTime 7 on it, you will need to download the QuickTime 7 software to view QuickTime VR. This doesn't replace your newer QuickTime, it just adds the ability to view additional QuickTime formats.
Unfortunately QuickTime VRs do not play back on iOS devices.