Short answer: yes, you can self-host on any computer connected to your network.

Longer answer:
You can, but this is probably not the best way to go about things. The first thing to consider is what you are actually hosting. If you are talking about a website, this means that you are running some sort of web server software 24x7 on your main PC. This will be eating up resources (CPU cycles, RAM) which you may want to dedicated to other processes (e.g. gaming). Also, anything you do on that PC may have a negative impact on the server software you are hosting. Reboot and your server software is now offline. Install something new and you might have a conflict bringing your server software down. Lastly, if your website ever gets hacked, then your main PC also just got hacked, and your life may really suck. This is why you often see things like Raspberry Pis being used for self-hosting. It moves the server software on to separate hardware which can be updated/maintained outside a PC which is used for other purposes. And it gives any attacker on that box one more step to cross before owning your main PC. Granted, it’s a small step, but the goal there is to slow them down as much as possible.

That said, the process is generally straight forward. Though, there will be some variations depending on what you are hosting (e.g. webserver, nextcloud, plex, etc.) And, your ISP can throw a massive monkey wrench in the whole thing, if they use CG-NAT. I would also warn you that, once you have a presence on the internet, you will need to consider the security implications to whatever it is you are hosting. With the most important security recommendation being “install your updates”. And not just OS updates, but keeping all software up to date. And, if you host WordPress, you need to stay on top of plugin and theme updates as well. In short, if it’s running on your system, it needs to stay up to date.

The process generally looks something like:

• Install your updates.
• Install the server software.
• Apply updates to the software (the installer may be an outdated version).
• Apply security hardening based on guides from the software vendor.
• Configure your firewall to forward the required ports (and only the required ports) from the WAN side to the server.
• Figure out your external IP address.
• Try accessing the service from the outside.

Optionally, you may want to consider using a Dynamic DNS service (DDNS) (e.g. noip.com) to make reaching your server easier. But, this is technically optional, if you’re willing to just use an IP address and manually update things on the fly.

Good luck, and in case I didn’t mention it, install your updates.