CERN, the European Organization for Nuclear Research, is the organisation that operates the European Laboratory for Particle Physics. Lots of experiments take place at this laboratory.

Stick to the official title "European Organization for Nuclear Research" for CERN websites. 

Use the acronym CERN in the singular: 

CERN offers student work placements (not "CERN offer student work placements")

Since CERN’s official name is the European Organization for Nuclear Research, write “Organization” with a capital O and a “z” when referring to CERN (“organisation” with an “s” in all other cases).

Why two names? A little background:

The name CERN is derived from the acronym for the French "Conseil Européen pour la Recherche Nucléaire", or European Council for Nuclear Research, a provisional body founded in 1952 with the mandate of establishing a world class fundamental physics research organisation in Europe. At that time, pure physics research concentrated on understanding the inside of the atom, hence the word "nuclear". When the organisation officially came into being in 1954, the council was dissolved, and the new organisation was given the title European Organization for Nuclear Research, although the name CERN was retained.

Today, our understanding of matter goes much deeper than the nucleus, and CERN’s main area of research is particle physics — the study of the fundamental constituents of matter and the forces acting between them. Because of this, the laboratory operated by CERN is sometimes referred to as the European Laboratory for Particle Physics.