Start writing about the gba struct

book/src/SUMMARY.md

@@ -9,3 +9,4 @@
         - [Mac OS setup]()
     - [Building the game](./setup/building.md)
 - [Learn agb part I - pong](./pong/01_introduction.md)
+    - [The Gba struct](./pong/02_the_gba_struct.md)

book/src/pong/01_introduction.md

@@ -13,3 +13,22 @@ You will learn:
 * How to add sound effects to your game.
 
 With this knowledge, you'll be well equipped to start making your own games!
+
+## Getting started
+
+To start, create a new repository based on the [agb template](https://github.com/agbrs/template).
+We'll call this `pong`.
+
+Then replace the `name` field in `Cargo.toml` with `pong`, to end up with something similar to:
+
+```toml
+[package]
+name = "pong"
+version = "0.1.0"
+authors = ["Your name here"]
+edition = "2018"
+
+# ...
+```
+
+You are now ready to get started learning about how `agb` works.

book/src/pong/02_the_gba_struct.md

@@ -0,0 +1,3 @@
+# The Gba struct
+
+Almost all interaction with the Game Boy Advance's hardware goes through the [Gba singleton struct](https://docs.rs/agb/latest/agb/struct.Gba.html).