Summarize this article:

It's the icon that resembles two silver gears.  Tap the icon on your home screen to open the Settings menu. It's next to an icon that resembles a compass. This turns the pop-up blocker on for the Safari web browser and blocks intrusive pop-up ads.

Summary:
Open the Settings  menu. Scroll down and tap Safari. Turn on the toggle switch  next to "Block pop-ups".