Can you use Kali Linux as the main OS?

It depends on the purpose of what you want to use. Kali Linux is a Linux distribution that is designed for professional testers and security experts.

If you are not familiar with Linux or if want to use for development, web design, gaming, etc. Kali Linux is not recommended you can use it as a virtual machine.

If you want to use for penetration testing, you can use Kali Linux as the main OS. If you just want to get familiar with Kali Linux, use it as a Virtual Machine. Because, if you face any issues using Kali, your system won’t get harm.

How make Kali Linux as main OS?

It is perfectly advisable to make it your main operating system, and many Kali users do. Simply plug in a USB stick running Kali, and as it boots select 'Install' rather than 'Live'. (If you're not sure how to make a Kali USB disk, just download an ISO file and burn it with Rufus .)