Can't start beginner tutorial: 'docker - command not found'

I just installed Grafana on a Raspi4 and wanted to start with the tutorial as described here: Grafana fundamentals | Grafana Labs
But I’m stuck at step 3 already: Docker not found:

Could anyone tell me what to do, please?

ok, and have you installed docker?

This makes sense, I’m just installing it.
Stupid in retrospect, but i’m new to linux and haven’t even thought about it.
So soon I should be able to continue with the tutorial, thanks

My next problem is: the sample application doesn’t work. I followed the first 5 steps up to here:

I think the two lines should show UP instead of EXIT:
tutorial-environment_app_1 /bin/sh -c /app http://db … Exit 2
tutorial-environment_db_1 /db Exit 1

In any way, when I try to access the sample application via pi-IP-adress:8081 the page is not available.

Same problem here also in a Raspberry Pi 4 with Rapsbian 10 (buster)

More info: App build error · Issue #5 · grafana/tutorial-environment · GitHub