First you have to understand CAP (Consistency, Availability and Partitioning, where you have to pick-up two of three) theory and our Business use case. MongoDB satisfies Consistency and Partitioning & Couch DB satisifies Availability & Partitioning.
Edureka videos in youtube regarding NoSQL are some of the best video tutorials.
https://www.youtube.com/watch?v=gJFG04Sy6NY
https://www.youtube.com/watch?v=KSq6tMMXZ8s
https://www.youtube.com/watch?v=3z1KFA2qcSo
Good presentations are available in slideshare.net
http://www.slideshare.net/quipo/nosql-databases-why-what-and-when?qid=3bb9f7f6-a53d-41b1-8403-cd6f181d0ca7&v=qf1&b=&from_search=1
http://www.slideshare.net/EdurekaIN/no-sql-databases-35591065?qid=f1b9c095-6d70-4d0a-91da-1df664c4f389&v=qf1&b=&from_search=3 (This presentation supports video tutorial in youtube)
