One of the easiest ways to manage your domain is to do it through CloudFlare (use their free plan). Setting up an A Record will allow your domain (or a subdomain of your choice) link redirect to your servers IP (assuming it has the default 25565 port). An SRV record allows you to make a domain redirect for your server if it doesn't have the 25565 port (ex: 26473).
First thing you'll want to do is to set your domain's nameservers to CloudFlare's. After you sign up for CloudFlare and complete their setup to add your domain, you should get a list of nameservers that you can use. Once you have those, log in to your BeastNode billing portal and navigate to the "My Domains" area. Click on the small down arrow next to the domain you want to edit and select "Manage Nameservers." Enter the nameservers that CloudFlare gave you and click "Change Nameservers." Allow up to 24 hours for propagation to take place. At this point, you can continue with your CloudFlare setup and it'll likely tell you to wait for propagation as well.
Once the above is done and your domain has propagated, log in to your CloudFlare account. Then go to your domain's "DNS" menu.
You'll be presented with the following entry box:
Note: All of these steps assume you want to create a subdomain to go to your server and not your top level domain itself. If you want your domain itself to go to your server (this would make it unusable for a website, so keep that in mind), just replace any part that tells you to enter a subdomain with the "@" symbol.
In the drop down menu on the left, make sure "A" is selected then fill in the info:
Name: Your desired subdomain (ex: play - this would make your domain redirect "play.yourdomain.com" - Leave it as the @ symbol to use the domain itself as "yourdomain.com")
IPv4 Address: Your server's IP (without the port)
Click Add Record when done. Remember that it can take a few hours for the changes to propagate and for the domain/subdomain to be usable to connect to the server (assuming that the nameservers have propagated also).
You can stop at this step if your server has the 25565 port. Otherwise, continue on.
Adding an SRV Record for servers without a Dedicated IP/25565 Port
If your server does not have a Dedicated IP/25565 port then you will need to set up an SRV Record to allow the domain/subdomain to redirect to the servers full IP:Port.
Return to your domain's "DNS" menu, then on the left drop down menu again, select "SRV" from it and you'll get a pop up:
Fill in the requested information as follows:
Service name: _minecraft
Name: Your subdomain name as you entered it for the A record section (just the subdomain part, without the domain, the @ symbol if you are using the domain itself and not a subdomain)
Click Save and you'll be presented with a second step:
Now fill in the following details:
Port: Your server's port
Target: Your full subdomain+domain (ex: play.yourdomain.com for the subdomain, or just yourdomain.com if you are just using the domain itself)
Click Save when done and click "Add Record" once the pop up goes away. You're now done! Just give it a few hours for DNS propagation to occur before using your subdomain to join your server.