How antimatter is created?

When enough energy is squeezed into a very small space, such as during high-energy particle collisions at CERN, particle-antiparticle pairs are produced spontaneously. ... When energy transforms into mass, both matter and antimatter are created in equal amounts.

Where do they make antimatter?

The first ever creation of atoms of antimatter at CERN has opened the door to the systematic exploration of the antiworld. 1. CERN, the European Laboratory for Particle Physics, has its headquarters in Geneva.