What is CERN?

I'm not a CERN employee, but the company I work for is connected with them, as well as many other scientific institutions around the world.
CERN is like most other particle accelerator laboratories, except that they have the world's largest synchrotron (the LHC). With that they can do science on scales that other labs can't do. They can smash particles together with so much energy that they can split them apart into even smaller things.

When it comes to the "miniature black holes" hoax and other crap like opening up new dimensions; that is impossible. Creating a black hole requires energies that are so incredibly high that it's essentially like trying to cram the entire Earth's mass into something the size of a ping-pong ball... and the smaller you go, the shorter the lifetime of the black hole. Anything more massive than 21.76μg (micrograms) can theoretically form a black hole (that is, 21.76μg would have a Schwarzschild radius of 1 Planck length). So when you're firing particles that have masses so impossibly small, you have no possible way of making a black hole, and even if you did, it would basically instantaneously convert all of its energy into heat and radiation.
Other dimensions.. well again you'd need to create wormholes or whatever, which require black hole levels of energies in order to create and keep 'open'. Even then we don't even know if they actually exist.