How to run Gitlab?

I’m new to using GitLab.
I have tried several methods of installing and running GitLab on my machine successfully.

But I want to work on configuring/coding/customizing Gitlab’s front-end by my own.
For that purpose I cloned the Gitlab Repo (hoping I would find the front-end Vue.js code there). I ran the docker-compose command, which took more than 3 hours of processing, but once after its done. I don’t know how to run the Gitlab server from the cloned Repo.

Or Is there another way to use Gitlab for the purpose I am trying to achieve? (Customizing/Coding the Gitlab’s front-end)

Any kind of help will be much appreciated.
Thanks in advance