just check this tutorial, there's everything explained regarding your question to setup and configure ngxinx and apache2 https://websiteforstudents.com/setup-nginx-reverse-proxy-apache2-ubuntu-17-04-17-10/

It's an older version of ubuntu, but I think there should be no difference.

Here the installation scripts of it:

Install Nginx

sudo apt-get update && apt-get install nginx

sudo systemctl start nginx.service
sudo systemctl enable nginx.service

Install Apach2

sudo apt-get install apache2

Nginx Config for IredMail

https://www.nginx.com/resources/wiki/start/topics/recipes/iredmail/

Like mention in the comment by @hextex, we need to know the port of your webserver to configure it correctly for nginx.

Nginx to configure multiple webpages

https://webdock.io/en/docs/how-guides/how-configure-nginx-to-serve-multiple-websites-single-vps

I hope this helps.