Best way to study a new type of database if you are experienced in another type

Does anyone have a good approach to learning a new type of database when they already are proficient in another one? I have thought about writing notes to myself about how to do various tasks that I am familiar with on the old db and showing the equivalent in the new one. For example, I like to read manuals. But should I just read through a manual without taking any notes or should I read a section of a manual that corresponds to something I know on my main db and write a quick document about what I just learned? If anyone has an approach that worked well for them I would love to hear about it. Bobby P.S. I am an Oracle DBA learning MongoDB.