Install a desktop
Depending on what you are going to use your Pi for, you may want a desktop environment to run graphical applications. Nevertheless, this step is completely optional.
First you need to ensure your packages are updated to the latest version, run:
sudo apt update
sudo apt upgrade
Then, you can use the apt install command to install a desktop environment.
Here are some popular and lightweight options:
sudo apt install xubuntu-desktop
sudo apt install lubuntu-desktop
sudo apt install kubuntu-desktop
Learn more about Ubuntu flavours.
Once the install finishes, reboot your pi with:
And your new desktop will come up automatically