New User, New Install, Newbie question(s)

Hello,

I’m taking at Rocket Chat for a potential solution to one of our objectives, and in the Docker documents, the following line(s) appear:

If you’d like to be able to access the instance directly at standard port on the host machine:

$ docker run --name rocketchat -p 80:3000 --link db --env ROOT_URL=http://localhost --env MONGO_OPLOG_URL=mongodb://db:27017/local -d rocket.chat

My questions are, the -p 80:3000 — that’s telling Docker (or Rocket Chat) to listen on port 80 rather than port 3000? Is this only telling Docker/RocketChat to stick to the change? I ask because I already have something listening on port 3000 that needs to remain until we get an alternative, like RocketChat up and running.

Also, how do we instruct Rocket Chat to listen on port 443 as well?

Many thanks,