There are two ways to write CGI programs in ScriptBasic. The old way is just like in any other language: the basic program can access the environment, the standard input and standard output. This is all needed to write a CGI program, decode the CGI parameters and create the http response.
The better way is to use the CGI module delivered with ScriptBasic that automatically handles CGI input, CGI environment variables, creates the uploaded files and even supports some security settings. For more details on the CGI module read the separate documentation of the module named CGI.