Basic syntax demonstration!

```erlang
-module(step02).
-export([double/1]).

double(X) ->
     2 * X.
```

* Statements are terminated with a full stop: ".".
* `module` declares the name of the module. Should match file name by default.
* `export` names functions to export out of this module. Will be usable by other modules. The `func/N` syntax means *the function `func`* with *N* arguments.
* `double(X)` is a function declaration and implementation.

Using this module looks like this:

```
1> c(step02).
{ok,step02}
2> step02:double(4).
8
```

* The `c/1` function compiles a module. Notice that it returns ok and a module name.
* To call the function, the module is explicitly named.