If you’re running Lubuntu 18.10 (Cosmic Cuttlefish), you don’t need to do anything. Snap is already installed and ready to go.
If you need to know which version of Lubuntu you’re running (except on 18.10), open the System Profiler from the System Tools desktop launch menu. Click on Summary and look for Operating System. Alternatively, from the command line, type
lsb_release -a.
Versions of Lubuntu between 14.04 LTS (Trusty Tahr) and Lubuntu 18.04 LTS (Xenial Xerus) don’t include snap by default, but snap can be installed from the Synaptic Package Manager (rather than the Lubuntu Software Centre) by searching for snapd (make sure your distro is up-to-date first).
Alternatively, snapd can be installed from the command line:
$ sudo apt update
$ sudo apt install snapd
Either log out and back in again, or restart your system, to ensure snap’s paths are updated correctly.
To test your system, install the hello-world snap and make sure it runs correctly:
$ sudo snap install hello-world
hello-world 6.3 from Canonical✓ installed
$ hello-world
Hello World!
Snap is now installed and ready to go! If you’re using a desktop, a great next step is to install the Snap Store app.