To create a internal clickable link in the same notebook:
Step 1: Create link
[To some Internal Section](#section_id)
Step 2: Create destination
<a id='section_id'></a>
To create link in one notebook and destination in another notebook.
Step 1: Create link
[To Some Internal Section](another_notebook.ipynb#section_id2)
Step 2: Create Destination
<a id='section_id2'></a>
If the notebook is inside a folder present in the current working directory:
[To Some Internal Section](TestFolder/another_notebook.ipynb#section_id3)