CNAME records (which stands for "canonical name" records) are used mainly to set up websites, but can be relevant for email or security/verification records as well.
CNAME records typically handle the setup of subdomains for your domain name, which would be addresses like www.mydomain.com or blog.mydomain.com. But CNAME records cannot be set up directly for a naked or root domain. (More information on alternatives.)
It is quite common for a domain setup to include a CNAME record and an A record. That ensures visitors can access your website using the www version or the "naked" domain. The service or platform with which you're setting up your domain name should provide the specific CNAME and other DNS records you need to add in your iwantmyname dashboard.
You will also need to add your domain name in your control panel for whatever service or platform you're connecting it to to finish setup and get the website or email working and online.
CNAME records can sometimes also be used for added security or to verify your account ownership. G Suite and Zoho Mail offer this option, for example. When setting up your email hosting, you create the CNAME record using a unique code you get from your Google or Zoho account, which that account can then detect to confirm that you are the domain owner.
Some examples, G Suite CNAME records, with calendar, docs, etc. for the different apps' subdomains:
Here is a Zoho Mail setup that includes the verification CNAME record:
The DNS records, including a CNAME and A record, for Big Cartel:
To learn more about CNAME records and other DNS records and their uses, check out our guide: What is DNS? Here's what you need to know.