python receiving data from a friend

I'm new to this whole shazam and I'm a little confused. I want to have a server receive data on my computer, and a friend send data on his own computer. The code for my server is as follows:

import socket

HOST = 'HOST' 
PORT = PORT    

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()
    conn, addr = s.accept()
    with conn:
        print('Connected by', addr)
        while True:
            data = conn.recv(1024)
            if not data:
                break
            conn.sendall(data)

I've blanked out the host ip and the port but I'm not really sure which one I'm supposed to be using for either tbh. The client code goes as follows

import socket

HOST = 'HOST' 
PORT = PORT   

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((HOST, PORT))
    s.sendall(b'Hello, world')
    data = s.recv(1024)

print('Received', repr(data))

So my server receives it only when I run the client, not my friend. My question is what IP and ports am i supposed to use? Where can i find these numbers? Why does it only work when I run the client and how can I fix this? And if anybody can direct me to some resources about this topic I don't know what to search up :( Thanks in advance!