Here is how to point a subdomain to an ip address using an A record in  your DNS manager.

A subdomain is a part of your main domain…. lets say I own domain.com a subdomain of this could be blog.domain.com or shop.domain.com Its what comes before your main domain.

To connect a subdomin to an ip adress and vice versa go into your DNS management for your domain name. This could be at Namesilo, Namecheap, Godaddy (avoid) etc etc.

You want to add an A record,  choose what your subdomain will be and the ip address. Dont worry about TTL at this stage. Submit it and it will take anywhere from 1 to 15 minutes to be live.

Now when you navigate to the sub domain it will be associated with the ip address you used.