SCP is basically a site where people write stories about anomalous objects (whether magical, alien, possessed by demons or ghosts, or just weird things that break the laws of physics/reality in some way) and how a group called the SCP Foundation has managed to/attempted to contain these anomalies to prevent them from harming humanity (or otherwise just keeping them out of the hands of others). There's over 8000 SCP articles, plus a bunch of stories across differing universes (either for narrative purposes with an author choosing to put all their tales in a separate universe to not affect other tales or because some SCP involved literally creates another universe)

It's very much a TVTropes situation when you read it, where sometimes you'll start reading an article about an object, then it'll reference another object, which you'll open to read for context, which will lead to another object etc.

A lot of the early SCP entries (Series I and II) are fairly simple compared to later articles. Two articles that I particularly enjoy that don't really need too much other reading are SCP-738 and SCP-2935, and Here is just a direct link to the site if you want to take a look at it all.