How can I partition the root mount point?

I switched to Linux(Ubuntu) first time two days ago. Now I'm trying to partition the disk for virtual machine use, but I'd allocated all space to root at installation. Is it bad practice? and how may it be fixed?

Here are screen shots in Gparted 1: https://i.stack.imgur.com/oDVqi.png
2: https://i.stack.imgur.com/hIHEs.png

Now I'm trying to partition the disk for virtual machine use, but I'd allocated all space to root at installation. Is it bad practice?

No, the approach to have a single partition for your system spanning the entire system is appropriate: that is how the installer would do it by default.

Think again why you would want additional partitions on your system. Having Virtual machines does not sound like a good motivation. Virtual machines live in a file stored in the file system of the host system. The space available in your partition will allow you to set up quite a lot of different virtual machines.

If you insist on creating additional partitions, you will need to reduce the size of your root partition. That can only work if the partition is not used, i.e., if the installed system on it is not running. You can do this using Gparted running in a live environment started from the Ubuntu installation DVD or USB.