I am trying to host my first website + service.

#My server setup

I have a static webpage in server 1. A gotosocial installation in server 2. They are connected to a reverse proxy (server 3). This has a public IP of (not exact) 204.230.30.104.

#My router setup

I can open ports 80 and 443. I just don't know to which IP (I'll explain why down).

#My registrar

In have a domain, say 'newexample.com'.
The @ has an A record for the IP (not exact) 208.145.80.33

#My confusion

1. If I want to make a subdomin for GoToSocial like 'gts.social.new example.com', do I use CNAME or A record?
2. If I want to serve the static website to be served at 'www.newexample.com' , do I remake an A record for www.newexample.com ?
3. There appears to be a CNAME in my DNS record already by the registrar for www that goes to some "redirect" link. What's up with that?
4. How do I make the domain connect to my server and how to make the server connect to my domain properly?