Short version, it's an app that infects people who look at the screen so they begin to be able to see SPC 1471. First only in digital images, i.e. take a photo of the room and the infected person can see the SCP sitting on the chair, but no one else can see it.
Then gradually you start being able to see them in other places. Out of the corner of your eye, reflective surfaces, etc. If you turn around the room looks empty, but hold up a mirror and you can see the SCP standing behind you.
After a time you can just see the SCP directly. He's just there in the room like any other person, but you are the only one who can see he/she (depending on main or subspecies version) exists.
In the origional context the SCP has no harmful relationship. It's not out to hurt anyone, he's just kinda...there. Follows you around, maybe curious about what your doing. Imagine a 7 foot bipedal dog that's invisible to everyone but you.
Varacung has made a change in the premise and the SCP is actually an emotional support app, who does his/her best to provide you comfort and take care of your mental health, and 'talks' to you by sending text messages.
An SCP, not related to mlp at all. Short version, it's an app that infects people who look at the s
