Please read the WordPress Domain Mapping and WordPress subdomain mapping documentation first. You will still have to change to the Cloudflare nameservers at the registrar for your domain in order for the site site to point to Cloudflare (these will be assigned when you add the domain to Cloudflare and go through the registration steps). You will need to make the changes below in your Cloudflare DNS settings for the domain.
-The default scanning process from Cloudflare will pick up multiple A records for your domain and the A records for the domain should be deleted.
**Important:** You do not want to delete other records, such as mail, MX, etc.). You would only want to delete the multiple A records for the domain that look like: A yourdomain.com IP address
-You would then want to create a CNAME record that points your domain to lb.wordpress.com. The CNAME record would look like:
CNAME yourdomain.com is an alias of lb.wordpress.com
For instructions on how to do this you can see the How do I add a subdomain article.