How exactly is a Ruby application architecture?
What are the different filetypes and their content?
What is the extension for a solution/project file?
Which file is analogous to a config file?
Are there files like DLLS formed?
If there is not a main() defined, what is the entrypoint for a program?
I looked up on the internet for all of this. But all I could find are some command line tiny code snippets or some tutorial to put Ruby on Rails.
No. Ruby is an interpreted language much like JavaScript, Python, and PHP.
Well, what do you define as an entry point? If you mean running a particular file, then anything not wrapped in a class or method will be invoked.
I strongly recommend you start by getting a better understanding of what Ruby is and how it works before moving on to rails. You can either buy a book or the notorious Pickaxe book is online for free here.