So I have already made the GUI and the program and all, and I want the option to enter an ip address on 2 computers in different networks (i enter his and he mine) and that we they communicate logs.
Both computers compute something and need to compare the values they compute, so i want to send arrays back and forth.
All that works already without the actual communication. I do not have a server I could use.
It doesn't matter in which network the PCs are for your program. You just need to make sure the packages are routed correctly, so that it is physically possible to access one pc from the other (via its ip address).
In your program you can just use a TCP connection with the TcpClient and TcpListener class to send your data back and forth. All information you need is the IP and Port of the PC to connect to.
A third-party server you mentioned is not necessarily needed if you have just two computers communicating in the same way all the time
