Previewing the front end image

I am using Windows 10.
I’m a newbie.
I don’t own the project but am a maintainer access.
I have added some new files to the main branch but want to view the frontend (what the page looks like to the end user) before committing it to the server to go live.

I tried using Web IDE, was expecting to see a picture of the page I’m trying to create but just saw the coding I had done.

I want to preview the front end page which could look like this :

I’m using GitLab Enterprise Edition 14.6.0-pre.

What am I doing wrong or have I misunderstood?

Thanks in advance for your help