Everyone wants a secure operating system. No one likes to have a computer infected with malware that slows down the PC, destroys files or steals sensitive information. Often, that operating system isn't very secure by default. If it's also a highly popular OS, such as Windows, then more tools are needed to enhance its security, simply because its default defenses will be targeted and bypassed by more attackers.
There's no security magic bullet, but using multiple layers of security can drastically lower the chance that your system will become infected by malware or be attacked by malicious hackers.
Some security tools are free, some are easy to use and others are so complex that a normal PC user couldn't possibly figure them out. What most PC users want is for their system to be protected "automatically" with minimal effort on their part. They don't want to tinker too much with complicated programs, and they would prefer not to pay too much extra to secure their computers.
I often help friends and family — usually, people who aren’t very technical — set up their new PCs and Windows installations. They always seem to ask me to "install an antivirus" as well. They know that there needs to be some "extra" protection on their PC to truly keep them safe, but they don't really understand what exactly is needed to achieve that. Therefore, they ask for a program that everyone knows protects PCs against "bad stuff" — an antivirus.
What they really mean, though, is that they want their PCs to be safe, regardless of which app or tool achieves that, as long as they don't have to bother with it after everything is set up. As such, I've looked for tools that offer as much protection as possible that are accessible by the vast majority of people. (It helps that the tools I've chosen are also free.)
In fact, most of the tools I'm going to mention require only slight or no tinkering at all after installation, or are very easy to use even by nontechnical users.
Some more advanced and complex software may offer stronger protections, but if the users don't understand how to use it properly, or they don't want to take the time to learn how to do it, they might just end up uninstalling it to save themselves the headaches.