This repository contains a Docker compose file for running Nextcloud with MariaDB. It contains a sample file with some variables that can be changed to your liking.
The docker-compose.yml file can be downloaded and saved somewhere on your drive or server. Make sure to have a separate folder for the configuration and data files. Change the volumes and environment to fit your situation.
You can launch the file with docker-compose up. After it has finished starting, which should not take very long, you can go to your browser and check if it is running properly.
You can check by going to 127.0.0.1:4433 if you're on the same machine. Replace 127.0.0.1 with the ip address in question if you have it hosted on another machine.
After you are sure that it all works, you can keep Nextcloud running in the background, just run docker-compose up -d.
For a more in depth guide on how this works, you can go to selfhostedheaven.com.