How to block pop-up?

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Surfing Internet is my new hobby. I have a problem with the pop-up that suddenly appeared infront of my internet browser. The pop-up like sreensaver and ads seem bit irritating me. Do I need to adjust my computer in order to block the pop-up? Im not expert about this computer system. Im scared if press some wrong button that will harmful my computer. Where should I go to block the pop-up?