To create a zone for your website against your Cloudflare account, you first need to create or link to your Cloudflare account
Navigate to the Cloudflare page for your website, you will not be able to set up a zone for sub domains.
On the Cloudflare page, click the "Set up Cloudflare" button, you should now have 2 options.
You will first need to select your account from the Cloudflare account drop down, this will be linked to the account you have already linked, but may also show other accounts for other people who have been added to the server, who may also have set up a Cloudflare account, you are free to choose any of the available accounts here.
You will then need to choose how you would like the configuration to be set up, from the Setup type drop down. The 2 options are Via Nameservers and Via Cname.
With Via Nameservers selected, click the "Create Zone" button. Your Nimbus Hosting server will then connect to Cloudflare and set up the website for you, it will also attempt to copy across any existing DNS records, and will set the zone to Paused by default.
If successful, you will be presented with a pop-up modal window that will give you new nameservers for you to update your domain nameserver records with, with whoever is your domain provider.
Your new Cloudflare zone for your website should now be set up.