Hi @AmmarHassan!
I’m not sure if there are guides published on developer.atlassian.com that make extensive use of Atlaskit in their UI. The getting started tutorial for a Jira Cloud app makes use of Atlaskit’s CSS, which is a gentle introduction.
If you’re interested in learning from other people’s code, I’d suggest one of these repositories:
If you’re interested more in learning from other developer’s experience, I’d recommend checking the following things:
@krzysztof.skoropada from Deviniti wrote a blog about their experience using Atlaskit to implement their apps on Medium: Building User Interfaces of Atlassian Apps with Atlaskit and AUI | Deviniti Technology-Driven Blog
@naiara from Comalatech presented at Atlascamp about moving from AUI to Atlaskit in their apps, too: https://www.atlassian.com/atlascamp/watch-sessions/2019/advanced-app-development/from-aui-to-atlaskit-streamlining-development-for-server-cloud-apps
In case you wanted to use Atlaskit in Server, too, @scott.dudley from Cenote Labs gave a presentation to help you get started: Supercharge Your Server App's Front End with Atlaskit, React, Flow and More - YouTube
I hope that gives you a few leads to get off the ground!