You need to visit the Zerotier website ; and register as a user ; you will then be able to create a VPN network and also access the API documentation.
What I need is a windows forms .net vb program which will utilize the API and expose all it's functionality. At the windows API page on the Zerotier website on the left hand side (panel) you will see what the API can do.
You will have to create one form or more for every API call.
Feel free to discuss with me over freelancer chat if you have any queries.