Like you're on a new device or borrowing a computer, and you open a webpage - and literally every website blankets your screen with ads every-which-way and all kinds of permutations of springing up to try and get you to accidentally click on something. The actual news article or whatever is just an afterthought.
Literally - how the fuck do people use the internet without an adblocker.
uBlockOrigin is still the gold standard for desktop adblockers. Though do go into the settings and turn on the anti-anti-adblockers.
For mobile firefox supports add-ons and uBlockOrigin.
For YouTube on mobile - YouTube vanced works.
Gold standard for getting rid of mobile ads is rooting the device, and putting ADaway on there - but a lot of times the phone manufacturers will be assholes and not push security updates and the like if it is.