The browser is the window through which you look at the whole internet - and through which it sometimes looks back at you.
Click the browser's icon, and a window opens with an address bar at the top. You type a word or an address, hit enter, and a page appears. Everything you see after that - news, mail, your bank account - passes through that one program. It's the go-between, your computer and the other computers where the sites sit.
The easiest way to picture it is a window into someone else's house. You don't go inside and carry anything home. You stand outside and look through the glass. When you close the tab, the window simply disappears, but while it's open, you see what's inside, and sometimes it sees you too.
The difference from before is that now you do almost everything through this window. You write a letter in Google Docs, without installing anything. You video call the grandkids. You pay a bill. You watch a movie. Once, every one of these was a separate program on your computer. Now everything lives in the browser, in separate tabs side by side.
That's exactly why the browser is a favorite target for people who want to harm you. Not because the program itself is weak, but because everything valuable passes through it - your passwords, your photos, your bank information. If someone tricks you into opening the wrong page or pressing the wrong button, they don't break into your computer by force. They just get you to open the window into their room yourself, instead of into the real bank.
Sounds logical, but
I spend my day inside the browser more than anywhere else. That's where I write code, where I talk to my AI tools, where I send files. And that's exactly why I know: let someone through that window, and they get through my whole workday - not just one program.
So I treat every open tab like an open window. I close it when I don't need it. I don't open a new window into a room I don't know - meaning I don't click a link I'm not expecting. A little care here saves the big problems later.