OpenVPN client - server through Internet

Hello everyone, I'm really sorry I'm new into all this networking stuff and I have issue understanding one thing about VPN connection.

So let's say I have a client on my local network with IP address of 192.168.2.100 and my external IP is let's say 90.90.909.909.

My server is in different city with IP address 192.168.3.100 and external IP 09.09.090.090.

They are not connected by any means at this moment - they are just 2 PCs in their own networks.

I have issue getting my head around which IP addresses I need to use while setting OpenVPN up and how to route data to the devices accordingly so I would honestly appericiate any help. Also, to be clear, this is just for personal use, it's not company or work related.

Thanks in advance, I hope this is the thread for it, I was looking for newbie networking but I didn't find it.