This isn’t really the place to be asking these kinds of questions because it’s not specifically TT-RSS related. You can search sites like stackexchange, etc. and they’ll have tons of examples to get you going.
Using Nginx as a proxy is pretty straightforward. If you have TT-RSS setup and working in Docker you just need add a virtualhost to your Nginx setup with something like:
location / {
proxy_pass http://0.0.0.0;
# include proxy_params;
}
proxy_pass can point to anything but usually you would use the IP (of your Docker instance). You may want to include a few more things in the location section. I know Debian ships with a set of predefined parameters that you can use with include proxy_params;. These include some common things for setting Host and Forwarded values (I commented that line for those who are not on Debian and copy/paste, so just uncomment it if you’re using a recent version of Debian).
In your TT-RSS config, you should define the SITE_URL to be the public facing name; that is, the name the reverse proxy is using, not the name or IP the Docker instance is using.
I use Linux containers versus Docker but my setup is basically the same: With TT-RSS running in its own container and a proxy running separately that forwards. If you have Docker specific questions others here can answer those, but look around on the Internet for Nginx reverse proxy, there are tons of tutorials.
e: Just to add, you’ll need to post some excerpts from your configs if you need more help. It’s difficult to figure out things like redirecting without seeing a bit more of your setup. (Please replace domain names and external IPs with generic information.)