There is a book called JMonkeyEngine 3.0 Beginners Guide that will walk you through all the different aspects of making a game. From start to finish, you build your own game. The book makes learning the engine very digestable.
The book is only 300+ pages but by the time you’re done, you will understand how much effort a simple game requires, and thus how much effort a big game would require.
After that, you can get the JME3 Cookbook which you can use as a reference when building your own game.
And maybe if it doesn’t fall on deaf ears, this too:
http://natureofcode.com/book/introduction/
Such a wonderfully written book. Everybody should read it.
Really amazing book. 
@jayfella thanks for introducing it.
Edit:
There is also a video series for the book
how much money one can make after developing a game like mynthruna
if you are lucky
If the game is good, more people pay for it and you get more money. If it’s bad, people won’t want it and you won’t get money.
good answer
Well I would add: If the game is good and you’ve been brilliant promoting it… then you might get money from it.
I guess you wouldn’t want to know the non diplomatic one.
now ur talking mr nehon
if the promotion is good
competetion all around
just the answer i want to hear
and thats clear my all doubt
This almost sound like a modern poem
and you don’t have to have Mythruna’s complexity to get money… Flappy Bird, yay!
is 2d game is as fascinating as 3d game
Let me break it down for you.
@azhar had developed 2 games. The first one, dubbed “3d game”. Then the second one, dubbed “is 2d game”.
The post above is promoting “is 2d game” by saying that it is as good as the previous one, “3d game”.
What a peculiar name for a game; I guess you need to stand out with something these days 
I guess he doesn’t like branding like others here
@all: Maybe we should not make fun of him because of his English skills
@azhar: Maybe you should try to come up with an actual question and put some effort in writing your post if you want to avoid this kind of answer