tour: split the first task into 3

tour.md

@@ -21,7 +21,7 @@ You will need the following to build Teliva:
 * Some fluency in typing commands at the terminal and interpreting their
   output.
 
-## Task 1: getting started
+## Task 1: running a Teliva app
 
 Read the first question in [the Readme](https://github.com/akkartik/teliva/blob/main/README.md).
 Try running the commands to download and build Teliva. If you have any trouble
@@ -39,20 +39,73 @@ number on screen. Hit `enter`. The number increments by 1. Hit `ctrl-x` to
 exit (press `ctrl` and `x` on your keyboard at the same time).
 
 Try editing the app by hitting `ctrl-e`. You see a "big picture" view of the
-app. Can you figure out how to modify this app to increment by 2 each time you
-hit `enter`? Don't be afraid to experiment. The menu at the bottom always
-shows the hotkeys available to you at any point in time. Don't worry,
+app. Spend a few moments scanning this page. All programs consist of data and
+_functions_: code that operates on data in some way. Teliva apps always start
+by running the special function `main`.
+
+Try browsing to some of the names visible on screen. Don't be afraid to
+experiment. The menu at the bottom always shows the hotkeys available to you
+at any point in time. Don't worry, everything you do can be undone.
+
+## Task 2: modifying a Teliva app
+
+The [first section of the Lua book](https://www.lua.org/pil/1.html) starts
+with this one-line example:
+
+```lua
+print("Hello World")
+```
+
+Can you figure out where to add this line to the app's code so it's visible
+when the app runs?
+
+Start by looking inside `main`. Most Teliva apps tend to share a basic
+structure in `main`:
+- some initialization, followed by
+- a loop that repeatedly updates the screen and then waits for the user to
+  press a key
+
+Can you map the lines of `main` to this structure? Which function describes
+how the app updates the screen?
+
+Some hints:
+- The function responsible for updating the screen is `render`.
+- `render` begins by clearing the screen (`window` in Teliva).
+
+After you make a change, can you figure out how to run your program?
+
+Does it do what you expect? Feel free to edit your programs as often as
+necessary. Programming is just long sessions of repeatedly editing (`ctrl-e`)
+and running (`ctrl-e`) your program.
+
+Once you're happy with your change, try exiting Teliva and restarting it with
+the same app. Do you still see your changes?
+
+You could save the file `counter.tlv` anywhere you like at this point. Or
+share it with someone else. Everything needed for the app is in that file.` If
+you get stuck or have a question, [send it to me!](http://akkartik.name/contact)
+
+## Task 3: variables and arithmetic
+
+Can you figure out how to modify this app to increment by 2 each time you
+hit `enter`? Again, don't be afraid to experiment. The menu at the bottom
+always shows the hotkeys available to you at any point in time. Don't worry,
 everything you do can be undone.
 
-Check out some of the short sections from [the Lua book](https://www.lua.org/pil/contents.html):
-[getting started](https://www.lua.org/pil/1.html); [assignment](https://www.lua.org/pil/4.1.html);
-[what you can do with numbers](https://www.lua.org/pil/3.1.html).
+Divide the problem into two parts in your head: where to make your change and
+what change to make there. You've already gotten some practice selecting a
+place to modify in Task 2. Repeat that process. Go back to the `render` page.
+What is the name of the _variable_ (box containing a number) that decides what
+number gets printed to screen? Go back to the big picture. Where is this
+variable defined? How does it get modified when you press `enter`?
+
+If you're stuck, some short sections from [the Lua book](https://www.lua.org/pil/contents.html)
+might help at this point: [getting started](https://www.lua.org/pil/1.html);
+[assignment](https://www.lua.org/pil/4.1.html); [what you can do with numbers](https://www.lua.org/pil/3.1.html).
 
 (Buy the Lua book to support the creators of Lua. Teliva is a tiny molehill on
 the mountain of awesome that is Lua.)
 
-Once you make a change, can you figure out how to restart the app with your
-changes?
-
-After you've made a change, try exiting Teliva and restarting it with the same
-app. Do you still see your changes?
+Some hints:
+- The function responsible for processing keystrokes is `update`.
+- The variable that tracks what number to print on screen is `n`.