[chunkyfunky]

Not sure how Spring does it, but for example in ASP.Net Core, it's really simple. In the app startup class there is a method that's automatically called by the framework whereby it supplies a services container. In this method you "wire up" your interface->concrete mappings

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddScoped<IMyDependency, MyDependency>();
  }

Later on when for e.g. an APIController is instantiated, once you've declare a constructor dependency on IMyDependency, it gets resolved for you automatically and whatever concrete class is mapped to gets created and passed to the constructor.

Outside of ASP.Net (console app for example) you can either do this manually, or you can get a ServiceCollection object from the framework, or you ca nuse a 3rd party DI library, etc.

Generally speaking if you don't configure this correctly you get a pretty simple message telling you that the container could not service the request for an IMyDependency or whatever and then it's pretty simple to figure out what you missed in the wire-up.