Whenever an ubuntu VM or an ubuntu server are set up, it is quite rare to get the GUI as default. But if you want to VNC or RDP, you might need one.
sudo apt-get install tasksel # tasksel manager to install GUIs
sudo apt-get install slim
sudo apt-get install lightdm
sudo tasksel # UpDown to navigate, Space to select, Tab to OK, Enter.
sudo service slim start # start display manager -- slim
sudo systemctl set-default graphical
sudo systemctl start gdm3
sudo reboot
This should allow you to login the computer with GUIs.