Welcome to the community!
For the most part, it's a roleplay forum. So, coming up with an idea to roleplay or adventure is typically the name of the game, and then inviting others to join in on the prompt. Either that, or joining other roleplay campaigns.

Typically, a lot of roleplays are based around fandoms as well.
When it comes to horror, I think the SCP Fandom might help with that niche. 
There may also be Silent Hill Fandom RP's, but it wouldn't hurt to search for Creepy Pasta specifically.