Note: If you're not using standard DNS you can disregard this topic.
blockerDNS needs to know who you are when you make a DNS request so that the right blocking settings are applied. For DoT and DoH you don't need to do anything because you have a unique URL that includes your username. But for standard DNS, you need to associate your public IP address with your blockerDNS account.
To make things as easy as possible and avoid your needing to manually add your IP, your address is associated automatically—and highlighted within your list—whenever you go to your account settings page. A side effect of this is that you can end up with a lot of temporary IPs on your list, but these are harmless. You can delete them or ignore them. In the future these will likely be automatically removed.
The automatic association is only done for your main profile and not for additional subprofiles. To associate an IP with a subprofile, add it manually. To prevent a subprofile's associated IP being automatically reassigned to your main profile you can click the lock icon.
Depending on your ISP, your public IP may stay the same for years or may change every day. In any case, you should set up dynamic DNS so that blockerDNS automatically always has your latest IP.
If you're a little more advanced you can skip the middle-man and report your dynamic DNS info directly to blockerDNS.
Another option is to use a client app that runs on your computer and regularly lets blockerDNS know what your current IP address is.