This might be a stupid question but

I linked the video I’m gonna talk about. Anyways, I watch a lot of scam bust videos and informational videos that talk about all kinds of scamming schemes on apps like discord or just your average pop ups. I was watching a video of a guy who downloaded a shit ton of scammy pop up ads and let them take over his computer. I’m wondering how he can save his computer from this? It’s probably a dumb question and I’m just not thinking about it and it’s probably something really basic like just activating some malware protection afterwards. But yeah idk sorry it’s dumb I guess I just am confused how he’s able to download all of these harmful things without any of it breaking his entire computer or breaching his privacy, and then removing the scam downloads afterwards. Sorry if this is stupid again lol