Understanding docker, NextCloud and nginx-reverse-proxy

Dear all,

I am not sure if I am right here and I fear this is a question that has been asked over and over - however, I did not find an understandable answer yet. Probably my issue is just a lack of understanding how certain things work with Doker.

I have the following situation: I would like to install NextCloud with nginx as reverse proxy and ideally Let’s Encrypt integraiton for https. However, I have already issues with the reverse proxy. I am running the following to set up my environment:

docker volume create nc_ext_db
docker volume create nc_ext_html
docker run -d --name nc_ext_nginx-proxy -p 80:80 -v d:/temp/nc_extern/docker.sock:/tmp/docker.sock:ro jwilder/nginx-proxy
docker run -d --name nc_ext_mariadb -v nc_ext_db:/var/lib/mysql -e MYSQL_ROOT_PASSWORD= --restart always mariadb
docker run -d --name nc_ext -p:8889:80 -v nc_ext_html:/var/www/html --restart always --link nc_ext_mariadb:mysql -e VIRTUAL_HOST=something.org nextcloud

Now my understanding was via the reverse proxy I should be able to reach my web site via the domain name, but it does not work. How would the proxy know that it needs to forward the request? I hope my question makes somwhat sense and is in the right place. If not, sorry for that - please let me know and I look in a different place.