Can't see any craft/app folder
I'm inferring from that last line that you're trying to install the Happy Lager demo.

However, that demo is currently only compatible with Craft 2.

The app folder was removed in Craft 3. And the demo has not yet been updated for Craft 3.

So if you really want to play with the Happy Lager demo, you'll need to download Craft 2. Or visit demo.craftcms.com, which will spin up a full copy of the demo for you.