Imagine you want to have your own piece of land to build your own house on. Before you can build your house, you need to buy the land and register it under your name.
In the same way, if you want to create a website, you need to register a domain name – this is your website's "address" on the internet. So, just like buying a piece of land, you have to purchase a domain name and register it under your name.
Once you have registered your domain name, no one else can use it or take it away from you. You get to keep it as long as you continue to renew it every year.
This way, when people type in your website's address or click on a link to your website, they will be directed to your website and nobody else's. Just like when people visit your house, they come to your address and no one else's.
So, in short, domain registration is the process of buying and registering a unique name for your website, so that people can find it easily on the internet.