What is the difference between Mobile Data and Data Roaming? I just need some explaintions regarding these Mobile Data and Data Roaming. Turning-on the Mobile Data alone won't let me go online. So, I need to enable the Data Roaming first before my Smartphone can go online.

Questions:


What's with Data Roaming? Why I need to turn-on the Data Roaming before I can go online?
What's the difference between Mobile Data and Data Roaming?


I would be happy if someone can answer my queries. Thanks :)
Both are the same except Roaming is when you get your home carrier data connection using onather network. The same apply for calls. 

Usually using your phone on roaming can cost additional fees so always contact your carrier for informations.