1. Create a Cloudflare account
To get started . sign up here
2. on the add site page add your domain

3.Select the plan you want

4.change the Proxy status to proxied and add your vps ip
see the image above

5.Update the nameservers

Copy the nameservers that cloudflare gives you and point your domain to them using your domain dashboard
Ex :
see the image above

6.Update the SSL settings
Go to the SSL/TLS page and select Flexible and then wait a bit so the settings gets applied

Congratulations you have HTTPS now