Today I installed Ubuntu and Lazarus IDE (Delphi style cross-platform IDE). I don't know anything about the file structure of Linux Operating Systems. Do you know some tutorials that can get me started specially with Lazarus, and does Linux have modules and API's or how does it work?
Some general info:
In Linux (almost) everything is implemented in libraries, have a look at dpkg -l | grep lib. All Debian packages that start with lib are library packages that install a library to /usr/lib or /lib.
Often there is a lib*-doc package for the library that contains its API documentation. Package documentation in general is installed to /usr/share/doc.
There may also be help availabe in the manpage system, try man man and in the GNU info tool.
C/C++ headers are located at /usr/include, you'll have to translate them to Pascal in order to use the libs.
Of course Lazarus and FreePascal come with there own libraries as well and you may want to look at them first.
There is also an Ubuntu specific StackExchange site here: https://askubuntu.com/