Working of .Deb Files , Compare with .exe files in Windows

[Jatin Davey]

Hi all

I am new to ubuntu. When i download any apps on the internet to be 
installed on ubuntu i get to download .deb packages. I know that these 
are the files that have the required application. I want to know the 
following:

1. What are the contents of any .deb pacakage in general ?
2. What happens when it is installed ? (Where are the files installed , 
Directories)
3. Any application under linux is launched using a script which is 
similar to an exe file in windows , based on this i want to know whether 
an application can be installed anywhere and in any directory and it can 
be launched from there without having to set environment variables.

Any pointers to all this would help.

Thanks
Jatin