Step 1: Open VirtualBox, click new, put details as shown below, and click next
Step 2: Now Select RAM size and click next
Step 3: Click on “Create a virtual hard disk now”
Note: The first option is to install OS in the separate hard disc, the last option is to use the existing virtual hard disc file.
Step 4: I have select VDH(native file system for VMWare), you can select VDI(native file system for VirtaulBox) or VMDK
Step 5: Select “Dynamically allocated” for using virtualization technology, click next
Step 6: Can update VM file location, and allocated file size, I have allocated 10Gb which is enough for basic setup or could update it to 20Gb. It can be updated after the installation as well. Then click on “Next”.
Step 7: Basic setup is complete for VM, now start installation, by selecting the OS name and click on Start.
Step 8: Click on the small folder icon, and select the Ubuntu OS ISO file downloaded from the official website.
Step 9: Now follow the OS installation procedure as shown in the images below.
Note: If unable to install please follow the link for resolution https://webtechmonk.com/fix-installation-issue-ubuntu-18-04-in-virtualbox-6-and-windows-10/