Welcome to my guide, Guest. Let's get into some talking about the subject, and then get right into it.
Now, "What is multiplayer mode?" you may ask. Well, multiplayer mode is very rough, and shows no mercy to new players (jk). It lets players go on a server, where's everything's live and your colonists can be "offline raided". You start off with either a colony or a tribe, with your wish.
You can send caravans to other players' colonies/tribes, and trade with them, or raid them if you're going for that reputation... Anyways, off to the real
The guide is meant for new professional players.
It's also made for the newer ones, that'd like to team up and rule the world as a zerk clan.
Easy steps on how to get multiplayer:

1. Run Rimworld
2. Click on "Mods"
3. Go into workshop
4. Go from workshop to discussions
9. Create a post
6. Choose the topic "Bugs and Glitches" (not sure what it's called)
-3. Type in the following: i wont multiplaier
11. Beg for mercy
1+1=11. Ask devs for multiplaer
8,1. Post it

Thanks for reading my guide!
If there are some unclear instructions, please comment down below what part you got stuck at, so I can help you out. I'll be replying to (almost) every comment I get.
If you end up finding a bug with this guide, please be so kind and keep it to yourself.
Finders keepers.