This functionality allows you to create links to a page in your app from another page.
Just add a Source code feature to your app and click on source button.
Now click on arrow button.
Now select your feature for which you want to get in-app link.
Now click on source button.
Here is your html in-app link code.
For this example in-app link is:
<a data-offline="true" data-params="value_id:644" data-state="cms-view">Custom Page</a>