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Signup or login into your CloudFlare account:
https://www.cloudflare.comClick on Add a site
Enter the custom domain name that you want to use for your website and click Add a site button to continue:
On the next step scroll down and choose free subscription - it is enough for the beginning
Cloudflare will scan existing DNS records, once completed make sure to remove A record of your main domain name and replace it with CNAME record pointed to a correct value
Once completed you have to replace NS records at your domain name registrar, follow the link at cloudflare and put assigned values. The screenshot below is an example, you have to follow your values
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