The Objects panel is on the same panel as Fragments and Validation, but on a different tab.

It is the most often used and the most important panel. By default, you see all objects as a full size objects. This can be changed by selecting SMALL in the top menu of the panel.

The Small objects option is right when you want to see more objects at a time. By hovering over an object you can read the type of the object, and after you drag it to the canvas it will be dropped and appear as full object.

You can also change the visibility of the object by selecting VISIBILITY in the top menu of the Object panel. By clicking on the object, you can turn on/off the visibility of that object. When the object is grayed out, it is turned off and not visible on the canvas. 

Every object that has the visibility turned off is invisible when you click on the button Toggle surrounding objects located in the toolbar. 

There is a unique object called Navigation Symbol, that is present in all of the models.

With Navigation Symbol you can create an assignment/link with another model and then that model will become the parent.

Drag and drop navigation symbol to canvas. Click on Link New Model/Link Existing Model and link it with desired model. After this, Up toolbar icon will be enabled and you will be able to navigate to the linked model with the Up icon.