Kali Linux is one of the popular distribution of Linux and you can use it in Virtual box without having to format your main operating system.
First download oracle virtual box for windows through Oracle website then install it to your desired directory within your hard-drive.
Now open your oracle virtual box and click on new tab at upper left corner. ‘Create virtual machine’ dialog box will pop up write name as Kali, Operating system type as Linux and version as Debian 64 bit if you download 64 bit iso from Kali Website . Keep memory size as default 1024 MB you can change it later. Hard disk file type as virtual box disk image. Storage on physical hard disk as dynamically allocated. Choose where you want to have your virtual machine setup and the disk space you want to use. Now Kali VM is setup you have to load iso file to it. Right click on Kali choose setting and then go to storage tab . Select your Kali iso in controller: IDE empty tab and click ok. Now start the virtual machine by double click in Kali tab .
For further information : How to install Kali Linux in virtual box for Windows || #Window #VM #Kali