Seriously, don't do this. Although opening a port on your router is a fast way to get your server accessible from the Internet, it's also a fast way to get hacked.
If you're really, really sure you want to do this, open port 80 on your router, as well as forward port 80 to your Raspberry Pi's IP address, so that your server can be hacked accessed from the Internet.
And that's it! Your website should now be available to anyone with Internet access. You can test this by typing your network's public IP address into a web browser on a device that's not currently connected to your network, such as a cell phone with Wi-Fi turned off.
A Self-Hoster Is Born!
Congratulations, you're officially a self-hoster! It's too bad you've probably already been hacked.
Now that you've seen how easy it is to open your content up to the world, it's time to learn how to do it much, much more securely. If you stop your self-hosting journey now, those ninja internet hackers will find you. And they will hack you. h@ck h@ck h@ck