Cloudflare is a web security and networking service that has many tools that can speed up and protect your site.
Domain
A domain is the root of the address you type into your browser to go to a site.
Domains are purchased at a registrar, another internet service that manages domain name ownership according to ICANN rules.
Cloudflare is a domain registrar, but I currently use Name Cheap.
Nameservers
Nameservers are a DNS setting that routes a domain to a hosting service.
After creating the site in Cloudflare, it provides nameserver addresses to configure in Name Cheap.
The DNS can take anywhere from 1-2 hours to 2 days. Likely less than a day, but it depends.
DNS
Cloudflare will automatically scan for DNS settings and include them.
You can customize them further if needed.
HTTPS
Cloudflare should default to Flexible HTTPS, meaning it will try to use HTTPS with the user's connection, and may use it to connect to the origin server.
You can use full or strict HTTPS if you have increased security requirements.
WWW
I heard somewhere that using www is a best practice.
This can be done with a page redirect.