Setting up a server is a bit difficult for people who never did it. There are tons of tutorials i would like to present you and what you have to do to get it to work with otherworld.
example1: http://ark.gamepedia.com/Dedicated_Server_Setup
example2: http://ark-survival-evolved.wikia.com/wiki/Dedicated_Server_Setup

FOR PEOPLE THAT ALREADY HAVE A DEDICATED SERVER
1. Just Download the mod on your PC by ♥♥♥ it
2. Search the mod on your PC, its ID is 631838798
(i.e. C:\Programs\STEAM\steamapps\common\ARK\ShooterGame\Content\Mods)
3. Connect to your Server using FTP or FileManager
4. Copy the whole 631838798 folder and the 631838798.mod to the mod folder on your Server
(For me it is on Linux: /home/steam/ServerName/ark/ShooterGame/Content/Mods)
5. You have to Launch your Server with these commands:
Linux
./ShooterGameServer Otherworld?listen?MaxPlayers=6?bRawSockets?GameModIds=631838798 -server -TotalConversionMod=631838798 -log -servergamelog

Windows
start ShooterGameServer.exe "Otherworld?listen?MaxPlayers=6?bRawSockets?GameModIds=631838798 -server -TotalConversionMod=631838798 -log -servergamelog"

You also can set up a password if you want to play only with your friends by adding
?ServerPassword=xxxx?

ADVANCED:
There are some things you can use to improve the management and playing.
Here are some examples:
1. Set up a Adminpassword: ?ServerAdminPassword=$ServerAdminPassword?
--> now you can use cheats when you login in the ingame console by typing: enablecheats $ServerAdminPassword
2. Want a break?: Use cheat slowmo 0 in the ingame console for stopping the game for all.
"cheat slomo 1" and you can continue to play ;)
3. On your Server there are the lvls of all players in a file
found in Saved/SavedArks
they are named XXX.arktribe or XXX.arkprofile
You can delete them to force all others to create a new LVL 1 character (needs restart of the gameserver)