Well, the SCP game story is centered around the concept of containing strange and abnormal things. There are these SCPs which can be all sorts of oddities, like creatures with abnormal powers or objects with inexplicable properties. The story has a lot of mystery as the Foundation has to constantly figure out how to keep these SCPs in check, deal with containment breaches, and study them without getting killed or causing widespread destruction.
The main characters in the SCP game story are often the personnel of the SCP Foundation. They are scientists, guards, and agents who are tasked with containing the SCPs.
The SCP Foundation is purely fictional. It's a collection of imaginative and often creepy stories and characters that are made up for entertainment purposes and have no basis in reality.