What the heck is DNS?
When you type tree.nodehost.ca into your address bar it has to be translated into an IP address before a connection can be established.
What the heck is DNSSEC?
It's an acronym that stands for "Domain Name System Security Extensions". Or DNS Security Extensions. It's a relatively new system that was created to improve DNS security.
There is vulnerabilities in the DNS system that could potentially let hackers hijack the process mentioned above. This is bad because they can send people to their own website instead of yours.
DNSSEC digitally signs data so that you can verify its validity. DNSSEC ensures that you're connecting to the correct DNS record assigned to that domain.
Enable DNSSEC in Cloudflare
If you don't understand all the technical talk above don't worry about it. Cloudflare makes this process very simple and you aren't required to understand what's going on behind the scenes.