The default terminal, also known as a command line, is called LXTerminal and it’s launched from its icon on the desktop. Take a look at the official Raspberry Pi documentation if you’re unfamiliar with the terminal.
Enter the following into the terminal:
$ sudo apt update $ sudo apt install snapd
You will also need to reboot your device. This can also be accomplished from the terminal (and from the desktop), but make sure you save any open documents first:
$ sudo reboot