Just to add to the above:
Most modern browsers block 'standard' pop-ups by default. Using an ad blocker might help a bit as well though, so there's certainly nothing wrong with Eddie's suggestion above.
However, if pop-ups have got past the security features of your browser, the likelihood is that they're being generated by MALWARE on your computer. So you need to run a malware scan.
If you've already got the free version of Malwarebytes Anti-Malware on your computer, use that for the scan. Otherwise use this alternative product from the same stable:
https://www.malwarebytes.com/adwcleaner/
(Note: That software doesn't actually install itself onto your computer, so it won't appear in your list of programs. You need to run it from your Downloads folder).