When someone types your website's address, four things happen in about a second: their device looks up which computer in the world answers to that name (DNS), connects to that computer (the server), asks it for the page (a request), and receives back files their browser turns into what they see (the response). Every website, app, and API on earth is a variation of that loop.
The pieces, one by one
Your domain is a name you rent yearly from a registrar. You never own it outright; you renew it. Losing a domain renewal is losing the business address the whole world has memorized, and it happens to real companies every week.
DNS is the phone book that maps your domain to the machine that serves it. When someone "changes your DNS," they are changing which machine answers when your name is called. This is why DNS mistakes take sites offline instantly, and why control of your DNS account matters as much as control of your bank account.
The server is just a computer that answers requests, usually rented from a cloud provider like Google, Amazon, or Microsoft. "The cloud" is other people's computers with excellent electricity and staff. Your app lives there.
Requests and responses are the conversation. Browsers ask, servers answer. When a page is slow, either the question is traveling far, the server is thinking too long (often a slow database), or the answer is heavy. Performance work is figuring out which.
HTTPS is the seal on the envelope: it keeps the conversation private in transit. The padlock does not mean a site is trustworthy; it means the conversation with it cannot be read en route. Every serious site has it, and browsers punish those that do not.
Why a business owner should know this much
Because every web project invoice maps to these layers: domain and DNS (dollars a year), hosting (tens to hundreds a month for most small products), the build itself (the real cost), and the third party services the app talks to. And because every outage is one of these layers failing: renewal lapsed, DNS misconfigured, server down, database slow, provider outage. When your developer explains an incident, they are pointing at one of these five, and now you can follow the explanation.
The two account questions that protect you
Who controls the registrar and DNS accounts, and who controls the cloud account the app runs in? If the answer to either is "the freelancer who built it, personally," fix that this week. Ownership of those two accounts is ownership of your presence on the internet. Everything else, code included, can be rebuilt. Those two are the deed to the land.