how hosting and dns and domain name registrars work

Seriously, I thought it is no need to spend money for a domain name and hosting service and I can build my own domain name registration service and hosting service have my own domains for my website.

I have some knowledge about these. - Hosting means a service that gives us space to keep our website. - DNS means the service which convert domain names into ip addresses. But I have no idea how domain names are registered and where are they registered and how domain name registration work.

Please, tell me how these all things work. How domain name registrars like hostinger,google domains etc. work. please help me.