What does -p- tag mean in Nmap

I am learning about Cybersecurity using TryHackMe and I have a couple of questions regarding Nmap:

1. What does -p- mean in Nmap? For example when doing this: nmap -p- 10.10.57.197 --open

2. What is the purpose of using it together with --open?

I just get different result when using and not using -p- and --open and I couldn't find anything on the internet (if you can share some nice docs I would be really grateful!).

Thanks!