Where to insert code when creating a custom app in PHP?

[darshi_gilder1]

Hello
I'm trying to create shopify app using this library 

Shopify/shopify-php-api(https://github.com/Shopify/shopify-php-api/tree/c3b93d9212e2431a4c99afb50b48cd2b3e92a3a8)

To setup the app they've mentioned to initialise this
Context::initialize(
$_ENV['SHOPIFY_API_KEY'],
$_ENV['SHOPIFY_API_SECRET'],
$_ENV['SHOPIFY_APP_SCOPES'],
$_ENV['SHOPIFY_APP_HOST_NAME'],
new FileSessionStorage('/tmp/php_sessions'),
'2021-04',
true,
false,
);
But I'm confused here where to put this code? can you please guide me?
Thanks in advanced.