As part of the 5G-PPP Initiative, the Software Network Working Group prepared this white paper to demystify the concept of the Network Applications. In fact, the Network Application ecosystem is more than the introduction of new vertical applications that have interaction capabilities. It refers to the need for a separate middleware layer to simplify the implementation and deployment of vertical systems on a large scale. Specifically, third parties or network operators can contribute to Network Applications, depending on the level of interaction and trust. Different implementations have been conducted by the different projects considering different API types and different level of trust between the verticals and the owner of 5G platforms. In this paper, the different approaches considered by the projects are summarized. By analysing them, it appears three options of interaction between the verticals and the 5G platform owner: - aaS Model: it is the model where the vertical application consumes the NetApp as a service. The vertical application deployed in the vertical service provider domain. It connects with the 3GPP network systems (EPS, 5GS) in one or more PLMN operator domain. - Hybrid: it is the model where the vertical instantiates a part of its Vertical App in the operator domain like the EDGE. The other part remains in the vertical domain. A similar approach has been followed in TS 23.286 related to the deployment of V2X server. - Coupled/Delegated: it is the model where the vertical delegates its app to the operator. The NetApp will be composed and managed by the operator. This approach is the one followed in the platforms like 5G-EVE. In addition, the paper brings an analysis of the different API type deployed. It appears that the abstraction from network APIs to service APIs is necessary to hide the telco complexity making APIs easy to consume for verticals with no telco expertise and to adress data privacy requirements.