this really good question ^^ about making money there is many ways to do that but the most that people use selling the game ^^
here are some ways that i know :
1)free apps on ios and android get money from ads also some of apps keep putting ads everywhere until you hate them and pay the paid one :P
and i think this work on chrome and facebook as this (only ads).
2)some apps sell thier games so companies for example samsung bought angry space so they sold to all samsung users for free because the comapany bought it.
3)some of people make apps with fund or something like this i don't know the name on english and then they put thier names on credit page.
4)some games let you try it for a while then you should buy it to play full version
5) a store in game but i think this is ruin the game.except if the game has many users and almost no bugs.
6)normal paid app.
7)last but not least some people made a super powered game or app and some company pay the whole game from ideas,sounds,graphics and everything like : zynga bought draw something with 10 million and all other many from that game or app will go to that company.
*the new ideas always get paid very fast but some of ideas doesn't get mention i don't know why maybe the companies doesn't look for one person sutdio they want a complete studio so if they found bugs they can fix it easily..and games are usually not for making money but for making more powerful games as you can see some games start and end in next year because they didn't put the money in the project...
games is a sea everytime you learn you will lost ^^