To reduce CPU usage you need to put your thread to sleep.
Or else it will block by constantly loop in your while loop.
like this.
while(true)
{
if(File.Exists(Path))
{
}
Thread.Sleep(1);
}
For TCP communication you need a server and a client (or multiple clients).
Take a look at
TcpListener[
^] for server and
TcpClient[
^] for clients. Good luck.