Drupal commerce shipping module is complex, there are few moving parts that you need to consider when making custom changes to it. First there are shipment types which are associated with order type, this is usually done through UI, unless you also add order type programmatically.

Simple way to do this is to add form alter in a custom module like this

Ngrok is great tool, to set it up to work with docker and your specific localhost you need to have account, make authtoken command and then run following to receive both http and https versions of your local environment exposed to internet.

One of the reasons we are using services instead of plain classes is possibility to swap out class that each service uses.  So what we need to do is we need to create a new class that's overriding an existing service class, and then we need to alter the service container to use our new class.

Jquery is still standard part of drupal core and when using JavaScript or Ajax you will probably use Jquery and Jquery once function. Code can be found in core/assets/vendor/jquery-once/jquery.once.js  so you could look how it works. It is pretty similar as in D7, look at the comments on how to use it.

In drupal 8 plugins are everywhere, so to get most out of them you will sometimes want to alter them. If you look at definitions of each plugin manager, you will see that all of them have something specific in their constructors, it is the line below

To alter main content view of commerce summary you need to change results part of view, you can do this in different ways, one of it could be hook_preprocess_views_view or with some of the 

You are using get with fieldname and you are getting array as result, to get value as string, use getString() method like below

$entity->get("fieldName")->getString()

Lets first talk about what does hook_views_data_alter() do in first place. Views is a query editor, it queries DB, so this hook alters how our data is queried. As in views UI you add, fields, filters, sorts, relationships, here you will have an exposure of all DB tables you can make queries on and data on what to use for fields, filters and sorting.

This one is one of the bigger surprises in drupal 8. Form building is straight forward, basic OOP bases on symfony, but then you want your forms to be translatable, you are in for a ride. First you will need to have schema yaml files in install and schema directory.