There are a couple of things you need when you are creating your self-hosted WordPress website (my #1 recommended platform and the one I use for myself and all of my clients).
Think of your domain as the street address for your new online home. This is what you give out to people so that they know where to find you!
While there are many places you can register your domain, some that you have probably heard of like GoDaddy and others that are a little less mainstream. My favorite place to register my domains is NameCheap. There are always coupon codes available for purchasing a new domain (and even usually coupon codes for renewing them), plus they always have the best prices!
Below is a video to walk you through purchasing your domain so you know exactly what you need and what you don’t (no need to spend extra money on things you don’t actually need!).