If you are looking to forward non-www pages on your domain to www. Here is what you need to do.
- Login to CloudFlare and go to 'Page Rules' section of your domain.
- If the URL matches , in this field enter your domain information http://example.com/* This denotes all the pages under your domain example.com
- Pick Setting as 'Forwarding URL'
- In destination URL enter your URL Information with www , http://www.example.com/$1
- Click Save & Deploy
Note: For this setting to work, Traffic of your non-www domain must pass through cloudflare. You can check this in your DNS settings. You should have a CNAME record for example.com with active cloud. Shown as below.