Then, right click on the screen to interact. You're now in the command prompt. Type "help" to get started, then type "programs" to see the list of programs you can run, and try running some of them. Type "help" followed by the name of a program to find out what it does. When you're ready to start creating your own programs, type "help programming", then use "edit" to create programs or "lua" to just start entering code. All the programs and APIs you can call have their own help pages.
Want more? Build a Disk Drive next to your computer, and craft some Floppy Disks: