Lemon squeezy integration question(s)

Once I get this done I will do a write-up so hopefully others can benefit from my frustration. In the mean time, I have a question about something.

The docs have a section about creating a checkout and it is confusing me. In this following instructions, it says to "create a checkout", is this a new file I will need to create for this? Or multiple? I just cannot figure out where to put the snippet of code it's giving, or what file I should create for it, and then how to call that file. I've tried to put that code in a few different spots and then initiate a checkout with their supplied button code, but I am getting Undefined variable $checkout error, so clearly i'm missing something. Here is the instructions/code.

For example, to create a checkout for a single-payment, use a variant ID of a product variant you want to sell and create a checkout using the snippet below:

use Illuminate\Http\Request;
 
Route::get('/buy', function (Request $request) {
    $checkout = $request->user()->checkout('variant-id');

    return view('billing', ['checkout' => $checkout]);
});

Any tips? Thanks!