When coding Visual Studio, I can have multiple website projects, and to switch between them is as simple as opening each website project on the local drive.
I'm confused at how CodeIgniter handles this, it seems the programming environment is the actual install location (doesn't really have a "project" concept), and how do I start to code a new website while preserving the code of the previous one?
Is there a script to package a project and export, then import later?
Codeigniter's documentation walks you through managing multiple applications with one installation
As noted in the link above, after structuring your application folder,
Each of your applications will need its own index.php file which calls the desired application.
I would like to further explain that after you have duplicated the index.php file you will need to go into your base directories .htaccess file and add a few new rewrite statements to the file.
I have previously taken my application/controllers folder and added subdirectories for each application. The controller routing would have to reflect these changes.