In general, synthetic elements are created by making a new element whose number of protons is the nucleus is different than any other known atom.

Nobelium is made by bombarding curium atoms with carbon atoms. The curium particles get pushed into the carbon particles in a particle accelerator called a cyclotron. The cyclotron uses magnetic force to push electrons in a semicircular path. Then, the electrons are accelerated through the gaps in the magnetic regions.

This diagram gives a general idea of how the cyclotron works.