How to use snaps via the CLI and GUI?
It depends on the type of application. Graphical apps should be launchable from the Dash. So for example, if you install the calculator app with:
sudo snap install ubuntu-calculator-app
You should be able to:
Open the Dash by pressing the Super key or the Ubuntu button in the launcher
Start typing the first letters of "Calculator"
Click on the Calculator icon to launch the app
Note: if the icon does not appear in the Dash, you might need to log out and log back in. You should only need to do this the first time after you've installed snaps support on the desktop.
Alternatively, you can launch the calculator app from the command line:
ubuntu-calculator-app.calculator
Notice the syntax is $SNAPNAME.$COMMAND. If $SNAPNAME is the same as $COMMAND, as a shortcut you can simply run $SNAPNAME