I have set up my computer to function as a server. When it comes to registering a domain name, I'm unsure which DNS servers to specify. However, I do have a static IP address, which is 81.30.159.5 and my DNS servers are 81.30.159.4. These servers were provided by the domain registrar.
But how will the provider know which IP address to direct its queries to?

It's your provider who manages the DNS for your domain. Therefore, it's important that he/she registers your domain in both the forward and reverse zones on their servers. Additionally, you'll require a static IP address - commonly known as a "white" IP address - which the service provider can offer. Don't forget to discuss this with your provider too!