You can run it from an image without docker-compose but I'd recommend looking into docker-compose if you're not already familiar with it. @[email protected] has the idea right that it's just a powerful installation file and can automate your docker management process rather well if you're using it a lot.
You can build a container from an image but it's obviously more hands-on. Lemmy may have additional dependencies they include in the compose file that may not be present in the image source. but starting with something like