I create a new model with new content types and new content aspects. This is a xml file named alphaModel.xml which I put within C:\alfresco\tomcat\webapps\alfresco\WEB-INF\classes\alfresco\extension. After I create the alpha-model-context.xml in the same folder.
I read your data dictionary guide. But how can I know if my model is integrated ?
I just had a look and unfortunately there's no logging that can be switched on to show which models have been registered. I'll create a JIRA task for that.
You can configure the web client to use your new types in create, view and edit dialogs and see if they work. Or you can write some code to query the Dictionary for registered models i.e. call DictionaryService.getAllModels().