https://www.bybe.net/cloudflare-enforce-ssl-redirect-http-https/ has the full details.
To redirect to HTTPS, you need add a "Page Rule" for http://*example.com/* with the "Always Use HTTPS" option from the settings.
To redirect to www you need three "Page Rules":
http://example.com/* -> https://www.example.com/$1
https://example.com/* -> https://www....
If you don't have to ask users to send some personal info and don't have online payment function, then you don't need Full (strict) certificate.
As it should be evident by now, Full SSL will mean a completely secure connection. You will have a fully secure connection between your visitor and CloudFlare and also a secure connection between your web ...
You need to do two things.
You need to point the subdomain to Heroku using a CNAME. You do that by editing your DNS records. Since you are using CloudFlare as your DNS host, you need to add a CNAME through their interfaces. They have instructions for doing so here.
Add the subdomain host name to your Heroku account (or wherever you eventually choose ...