Following your link I found this guide:
https://support.cloudflare.com/hc/en-us/articles/205195708
As per instructions there, I registered in Cloudflare (for a free plan), added my site and added NS records in njalla dashboard that use Cloudflare's nameservers I was shown (now those are the only NS records I have set up). It appears that I will need to wait from 2 to 24 hours to see the results, so hopefully I understood the instructions correctly.