I hope you can find answers to all your questions here.

please see: Data Mining: Concepts and Techniques (The Morgan Kaufmann Series in Data Management Systems)

You can use it for image/video clips databases, e.g., Article Enhanced Hierarchical Clustering for Genome Databases

Chapter Hierarchial Clustering

Dear N. Syed Siraj Ahmed ,

Hierarchical clustering is the most popular and widely used method to analyze social network data. In this method, nodes are compared with one another based on their similarity. Larger groups are built by joining groups of nodes based on their similarity.

https://www.sciencedirect.com/topics/computer-science/hierarchical-clustering#:~:text=Hierarchical%20clustering%20is%20the%20most,nodes%20based%20on%20their%20similarity.

Regards,

Shafagat

You should seriously start studying statistics from the ground up.