In the world save folder, there's a "computers" sub-folder, and each computer/turtle gets its own numbered directory within that (to serve as the "drive" of each system). Typing "id" into the command prompt of a given computer/turtle will give you its ID number.
Files and folders within these "drive" folders show up on the ComputerCraft systems immediately, so you can simply drag data in / out on the fly. You can even use external text editors directly on these files.
If you're going with a multiplayer environment, on the other hand, then the world save folder won't be available to all players: it'll be on the server, so presumably you'll have access to it and no one else will.
The free
Pastebin site is usually used in such cases.
The pastebin script (available to all ComputerCraft systems by default) can be used to upload and download script files using their servers.
If you're using the Beginner Turtles from
ComputerCraftEdu (an addon mod for ComputerCraft), things are a little different: they're rigged to store information in a player's "library", as opposed to on the turtles themselves. Each player can approach
any Beginner Turtle and see the script files from their library. These library files are still stored in the world save's "computers" folder, and regular computers / turtles can be used in a world with Beginner ones, too.