on the Dynamics 365 menu, point to Model Management and select Create model.
Give a model name, publisher name , select layer and other values and press " Next "
Now here we can create a new package or select any existing package. We could create a new package and select the required package as referenced packages
As shown in the above screenshot i select the " Create new package " because i am creating a " Extension Model ".
Now " Select referenced packages " window appears. When you create your own package you can select from an existing package to add them as references in your new package. You may need to add some standard package reference if you want to add them into your customization. As shown in the below screen shot i select the " ApplicationSuite " and some other packages as a referenced package of my custom model.