Usually, this is straightforward: you visit 127.0.0.1:$PORT on your host system, done. Well, except when it doesn’t work.
You can, however, use internal WSL IP, which is always available. Type ifconfig in your terminal and grab the first IP in the inet row in the eth0 section. Use this IP instead of the local one above.
It may also occur that you need to explicitly tell the server to use this IP instead of the local interface. For example, for Zola, this is done by specifying the -i flag.