I can not understand appium and its port

I'm new in appium and I want to run my test by using it. I like to run it parallel and I can't understand what should I do exactly! I need to run it on several appium ports or just use the default port(4723)?

How can I execute it by several ports?!

Please help me it's so hard to understand different designing like:

1. Running multiple Appium servers, and sending one session to each server
2. Running one Appium server, and sending multiple sessions to it
3. Running one or more Appium servers behind the Selenium Grid Hub, and sending all sessions to the Grid Hub
4. Leveraging a cloud provider (which itself is running many Appium servers, most likely behind some single gateway)

too! I would be happy if someone could even explain each of them by drawing a figure =) My system is Ubuntu.