I want to install freeBASIC on ubuntu( to code QBASIC). There is a package "libfreebasic" which I've installed but I don't see any difference on my system... Can I code in QBASIC in ubuntu?
What you are looking for is a BASIC interpreter. You can code BASIC on any text editor. According to this post, the procedure you should follow is:
The real question, of course, is why in the world would you want to code BASIC? Even if you do have a valid reason for this, why in the world would you want to code BASIC in a Linux environment? There are many interpreted languages that are already integrated or for which it is very easy to install interpreters in the *ix world. The list includes, but is not limited to, Perl, Python, BASH, TCSH, Ruby, Lisp...
You can use QB64 as an IDE if you want to use QBASIC. (Yes, it does work on 32 bit platforms.)
In case you want to stick with FreeBASIC, you will need to install a few dependencies. Also, it's only a compiler, so you will need to create scripts using a text editor of your choice, then compile and execute them from a terminal, like so:
If you're looking for a full IDE specifically for QBasic, I don't think you'll find one. FreeBASIC is a compiler, which claims to be compatible with QBasic, but you don't use it for actually writing applications. You can write your BASIC applications in whatever text editor or IDE you'd like (I recommend Emacs, others may recommend Vim, Eclipse, or something else). Once you've written the application in the editor of your choice, you can use FreeBASIC to compile it on your machine.
However, you really might want to consider options other than QBasic. If you're set on using some form of Basic, you can use VB.Net, and compile it using the Mono VB.Net compiler. You could also try Gambas, RealBASIC, KBasic, etc.