How can I make my cinnamon desktop the default? No screensaver can I do a screen save?

I have installed cinnamon on my Ubuntu 18.04. I change to the desktop by terminal command $cinnamon --replace and I get the cinnamon desktop up but the terminal is still active.

I cannot do a screen saver with this how can I force a screen save?

How can I make this the default desktop?

I also want to boot up in this desktop as well is that possible?