The SCP Foundation is a secret organization dedicated to containing and researching anomalous artifacts and entities that threaten the normality of the world. The events of the game take place during a sudden containment breach at a site of the SCP Foundation, causing several Euclid-Keter SCPs to escape containment and wander throughout the facility.
There are several roles you can spawn as.
You're most likely to spawn as either a Class-D Personnel or a Foundation Staff.
In both cases, the same applies: to escape alive with all your limbs intact, you'll mostly have to run around this maze-like structure, trying to find things like key cards, useful items, or, if you're lucky, something like a weapon.
However, if you spawn as a Security Guard, your goal is quite different - to deal with the violation of the conditions of detention. Although you do not have the best weapon for this case, but it will be enough to slow down the threat until the arrival of better help and to contain the entities.
After a while, there will be a wave of the appearance of the Mobile Task Force, the Chaos Insurgency, and also, under certain conditions, the Global Occult Coalition.
The Mobile Task Force (MTF) is sent to deal with the consequences of a breach of containment, such as an armed Class D or the Chaos Insurgency.
The Chaos Rebels have a different goal: to free Class D and destroy all Foundation personnel and SCP objects.
The goal of the GOC is to completely destroy all life in the complex. Class D personnel, Foundation personnel, SCPs, and related organizations. They only arrive under certain circumstances.
All factions have good weapons, and almost all of the different roles in each of their factions. However, GOK is considered the strongest faction in the game, as it has better weapons by default than the others.
But you can also play as the SCP objects themselves, the choice is great, and your goal is simple - to kill all living things and work together with other SCP objects as a united team.