It took me a bunch of tutorials to get my multisite running, so I’ll save you time by putting what I did here.
These are steps from a bunch of tutorials I’m too lazy to find again, so I didn’t do all the hard work :). The one guide I did use a lot was DigitalOcean’s.
Anyways, the first thing you’ll need to do is make sure your web server is configured to accept connections on the particular domain you want the other site in your network to be. It should point to the same root directory as your current site, and have all the same options. I’m using nginx, so I don’t know what .htaccess files you might need to change if you’re on apache.
Now, go into your server, and edit the file called wp-config.php, which is in your site’s root directory. Right before the comment that tells you to not edit anything below it, add:
define( 'WP_ALLOW_MULTISITE', true );
Next, go into your WordPress dashboard, and click on the Network Setup option, which you’ll find under the tools page. Follow the instructions you see, and copy the wp-config.php options it gives you. Paste what you just copied into the wp-config.php file directly under the define( ‘WP_ALLOW_MULTISITE’, true);.
Just log in, and log out, and you can select the multisite icon(just left of your usual site options), and select network admin, then sites. Click on add new, and enter the information you want. If you want a domain that is not a subdomain, enter what you want in the first box, and after you create the site, go back to the sites page, and click the edit link that appears when you hover over the site. Now you can change the domain to whatever you want!
I could not log in to my new site, so I did some googling, and found that I needed to add the following just under all the other multisite settings:
define('COOKIE_DOMAIN', $_SERVER['HTTP_HOST'] );
Hopefully, you know have a working WordPress multisite!!!
If you have any problems, let me know down below.