Doing docker exercise, Help needed

Hi, so i’m pretty much a beginner willing to educate myself on docker, i found some exercises, and got stuck on one of them, Can some one help me out with it ?

Create a Dockerfile that starts with FROM devopsdockeruh/overwrite_cmd_exercise
and works only as a clock.

The developer has poorly documented how the application works. Passing flags will open different functionalities, but we’d like to create a simplified version of it.

Add a CMD line to the Dockerfile and tag it as “docker-clock” so that docker run docker-clock
starts the application and the clock output.

You can also find a github repo, Do i have to pull the repo ?
Or it is something really simple as adding CMD to the Dockerfile ?
I tried searching things like how to execute flags using dockerfile, but i think i miss something fundamental.

The whole page - .
If I posted it in the wrong place, please guide me where i can seek help, Thank you !