DNS (Domain Name System) records tell the DNS server where each domain should point to. There are a number of different DNS record types, example MX records which point emails (firstname.lastname@example.org) to the email host.
To point your domain to Webflow, you'll create 2 types of records: A records (you'll need 2) to point the root domain (domain.com) to Webflow and a CNAME record for each subdomain (blog.domain.com, help.domain.com) as well as the full domain (www.domain.com).
The Webflow records should point to the following addresses or values:
If SSL is ON (recommended) in your Webflow settings, the Webflow A record values should be: 184.108.40.206 & 220.127.116.11 and the Webflow CNAME record values should be: proxy-ssl.webflow.com.
If SSL is OFF (not recommended) in your Webflow settings, the Webflow A record values should be: 18.104.22.168 & 22.214.171.124 and the Webflow CNAME record values should be: proxy.webflow.com.
To connect your domain to Webflow, check out the Connecting a custom domain tutorial.