The Internet protocol stack is organized in layers. In order to transmit packets from one station to another, the concept of encapsulation is used. At the sending side, the packet is passed to the next lower layer, which appends an additional header to the packet and passes it again to the next lower layer. Thus the packet from the higher layer is encapsulated in the lower layer packet.
Encapsulation is shown in this application by an analogy. Instead of packets Russian dolls, so called matryoshkas, are transmitted from one house (station) to another one. Matryoshkas are a set of dolls of decreasing sizes that can be placed one inside another and thus, show directly the concept of encapsulation.
Additionally, the application allows you to select an intermediate system placed in the network during transmission. Try by yourself how many matryoshkas are removed and again placed over the smaller ones!