Digital Ocean droplet with Cloudflare - help needed

I need to move my domain name from GoDaddy to a new Digital Ocean droplet via Cloudflare.

I have already changed the nameservers in GoDaddy to those of Cloudflare, and have created a new droplet (basic with standard settings).

I'm getting a 521 error.

Please provide me with step by step instructions to get the domain working.

Once that's done, I need to access the droplet via Codeanywhere. Please provide step by step instructions so that I can upload my site files (straightforward html, js, css - not WordPress or anything like that).

Thanks